Some of the classes get a full Base Attack Bonus progression and others get the Half progression, leading to a 5-point gap at level 10 (all the classes max out at 10 now, because d20 Modern leans into the lego-block-style multiclassing mechanic, which is really something that needs its own paragraph). And that would be bad enough, but then classes also get a Defense Bonus progression and that ranges from +8 to +3.
I can see the advantage, from a gameplay perspective, of rebalancing attack and defense so that attacks hit on 8+ instead of 10+ (and, in fact, for Ukss Plus, I balanced monsters on the theory that heroes should hit on 7+), and I can see why, constrained as it is by 3.X's obsession with NPC-PC symmetry (almost all your antagonists in this modern setting will be regular humans with class levels) it leads to PCs getting hit more often (Ukss Plus math assumes PCs get hit by 11-12+). But I cannot, for the life of me, remember what the hell we were thinking, putting up with the 7-point gap between attack and defense. That's a to-hit on 3 or higher, for two equal level characters going head-to-head. And that's only for a single-class progression. If you look at a level 20 build with only a single multiclass, the gap is +20 to-hit vs +6 defense. Granted, that's a Strong Martial Artist fighting a Charismatic Personality (i.e. "celebrity"), but that's still ass-backwards design. Level 20 should mean something, damnit!
And, okay, maybe there's some symmetrical ratfucking going on because the Martial Artist needs to roll a natural 20 to resist the Personality's "Winning Smile," but even that's just the equivalent to a 1st-level Charm Person spell and it doesn't work if combat has already begun.
And that's comparing two very basic and obvious builds. Most of your d20 Modern characters are not going to be so straightforward. The underlying philosophy of the game is that you will frequently multiclass to narrow in on your own very specific character concept. This is encouraged by the nature of the basic classes. Rather than being based on jobs like "Fighter" or "Wizard," the six basic classes are each based on one of the six attributes: The Strong Hero (Str), The Fast Hero (Dex), The Tough Hero (Con), The Smart Hero (Int), The Dedicated Hero (Wis), and The Charismatic Hero (Cha).
This is what I was talking about when I said d20 Modern had some bold new ideas. The way the classes stake out a niche, allow for specialization into that niche, but then come together to give the player flexibility when making their character - that's inspired, like a hybrid of class-based and point-buy experience systems. And when I talk about the d20 chassis showing its age, I mean that the class-levels fail to do the one thing class-based systems are supposed to do (guarantee rough parity between characters of equal level) and most of the things you can buy with your points are simply not worth the expense (this book has an unprecedented number of the infamous "+2 to two different skills" feats as well as the original, terrible version of the Toughness feat).
I think you could make the argument that in a modern setting "combat" is more of a specialist niche than it is in D&D style fantasy, and so the fact that you can carelessly sink your BAB by injudicious multiclassing (with a crack build, you could have a +2 to hit at level 20, but even a fairly reasonable Smart 3/Charismatic 3/Field Scientist 4 character could have a +4 at level 10) might not be all that big a deal. Generally, these days, we don't fault the people who choose to have a well-rounded academic background for failing to train for pro-level MMA fights. But counterpoint: the GM chapter takes pains to explain:
"Why should a Smart hero's base attack bonus, for example, improve as he [sic] goes up in level? Because he [sic] goes up in level by participating in adventures, and adventures almost always involve combat of some sort."
Preach it. Love that "the story is what happens in the game" swagger. Just a quick follow-up question from my position of having 20 years of hindsight - if the Smart hero gets better in combat because they are primarily an adventurer who uses their smarts, why do they improve their BAB so little?
Because what's really going on here is that the Strong Hero has the same numbers as the D&D Fighter and the Smart Hero has the Wizard's numbers, despite the fact that the Smart Hero does not get spells and the Strong Hero's niche of melee combat would be considered quaint and archaic in the game's modern setting.
But I don't want to rag on d20 Modern too much. Its main weakness is just that it's a 22-year-old game that never got another edition, so all of its 3.0-era mistakes got frozen in amber, preserved so that a cynical blogger, decades hence, could call them out as if he (not "sic" because I'm talking about myself) were discovering some new and terrible flaws. My overwhelming thought while reading this book was "someone should make a spiritual successor to d20 Modern . . . wait, I'm someone . . . should I remake d20 Modern . . . no, no nobody wants to see that . . . do they . . . should I test the waters by sarcastically floating the idea in a parenthetical . . . eh, people would probably see right through that, better to put it on the wait list of potential projects that's already a mile long."
Needless to say, I loved this book.
It's also, for lack of a better word, the most generous book WotC put out in the 3.0 era. It is a complete core, with all the character stuff you expect in a player's book, an abbreviated, but thorough GM guide, and also a source of monsters, magic items (though I don't love that it refers to magic and psionics collectively as "FX") and three separate campaign models, each of which has two unique Advanced (i.e. "prestige") Classes. It's overall . . . 3.X-ness keeps it from placing on my list of all-time top one-volume rpgs, but it can never be accused of deliberately leaving something out. d20 Modern is packed.
The campaign models were attractive in their outlines, even if they sometimes felt like Store Brand World of Darkness (except "Urban Arcana" which felt like Store Brand Shadowrun). I expect that's as much a function of their brevity as anything else, though. They've each got 15 pages to sell me on a whole campaign world and so they rely a lot on the power of genre, but WotC's in-house style tries to stick to a soft PG-13 so it's hard for the genres to land.
"Shadow Chasers" is basically "Buffy the Vampire Slayer." The various D&D monsters are here in their most dangerous and evil form, they're called "Shadows" and the PCs chase them. And lest this seem too glib on my part, I'll point out that the introductory fiction contained the (apparently) unironic in-charcter dialogue: "Ready to chase some shadows?" It's all perfectly serviceable. Maybe a little on-the-nose, but it has the advantage of being instantly understandable and easily gameable.
I guess it's a little weird that, in lieu of spellcasting, the Occultist class gets a fixed number of randomly chosen scrolls every time they gain a class level, but I don't hate it as a mechanic in a low-magic setting. The basic body of the class probably needs buffing, though. It's built like a spellcaster but its spellcasting abilities are extremely limited. If you GM this campaign, you're going to have to drop a lot of scrolls as loot. Strangely enough, its counterpart, the Shadow Stalker would probably be one of the better Fighter prestige classes if backported into D&D, so maybe this is just what caster-martial balance looks like in a 3.0 context.
"Agents of Psi" I can't take seriously because it has the line "Reality is a construct create by group consensus" and I just have to shake my head and say, "Mage: the Ascension spent 25+ years and 70+ books failing to make that concept work, so get out of here with your 15-page mini-campaign." But aside from that, it's a sci-fi fantasy setting inspired by 90s conspiracy theories and media like The X Files where you play as government agents who must defend the Earth against aliens, genetic experiments, and rogue psionics all while keeping the truth from a general public who is not ready for the revelation. I can't help wondering if it's politically significant that White Wolf took this premise and cast the PCs as rebellious outsiders, but WotC's first instinct was that the PCs should be the cops. It probably isn't, but when considering d20 Modern as a whole I couldn't help but notice that heist capers are conspicuous in their absence.
The final campaign model is probably the one with the most potential - "Urban Arcana." In this urban fantasy setting, the Earth operates on a slow cycle of rising and falling magic (called "Shadow") levels. Over the past few years, the magic level has risen to the point where creatures of Shadow (the various D&D monsters) have begun to arrive in our reality from the mysterious far shores of Shadow. Unlike "Shadow Chasers" the forces of magic aren't intrinsically antagonistic and much of the drama of the setting is driven by the complementary processes of modern things adopting magic and fantasy things learning to use modern technology. You know, mischievous (but not evil) goblin stealing cars and taking them out for joyrides, despite not knowing how to drive. An illithid gangster with minotaur muscle. An ancient knightly order getting reactivated when its magic relics start working again.
But I won't say too much about "Urban Arcana" because it's got a full campaign book that is next on my d20 list, so I'll save my thoughts for when I see it in its final form.
Overall, I thought d20 Modern had a lot of potential as an offshoot branch of the d20 family tree, but without the campaign models it was probably too conservative to really do what it had to do. It wanted to occupy a niche of "cinematic reality," but it never saw that the most obvious use of its level system was to dial in on particular levels of action-adventure - everyman heroes and gritty thrillers at low level, over the top explosion and bullet ballets at high level. I think, if it had gotten a second and third edition, to keep pace with mainline D&D, it would probably have developed into one of the best rpgs out there . . . but it didn't get them, so I guess I have to file it away as an "almost was."
Ukss Contribution: I kind of hate that I'm doing this, not because the entry is unworthy on its own merits, but because my reason is almost entirely that the name rhymes, but I have to go with the Crystal Pistol. It's a neat looking device - a handgun whose top part is made of psionically active crystal. Instead of bullets it fires bolts of concussive telekinetic force. The Ukss version will be able to be recharged and will probably be the signature weapon of the moon goblins.