Change "superheroic" to "non-superheroic" in last para
Just as a point of interest, Green Ronin modified Mutants and Masterminds into the True20 system, which in some ways is a closer match for traditional fantasy or horror RPGs. It retains the "save against damage" mechanic (called Toughness) of M&M, but has levels like standard D&D (but only three primary classes, or "roles": Adept, Expert, and Warrior).
Originally Posted by Citadel
If I recall, someone even figured out how to derive True20 characters from M&M. So I guess if you want greater flexibility in character creation, go to M&M; if you want something a little more traditional for NON-superheroic play, go to True20.
(Note: I've yet to play either, but they both look interesting.)
Differences between M&M and True20
I'm not at home, so I won't give you a rule-by-rule difference, but here's a rough idea.
As a general rule, the intent of M&M is to build and play superheroes, with superpowers and gagdets and so on. True20 cleaves more closely to d20's roots: classes, levels, feats, and skills.
M&M characters start with a point budget roughly correlated to the "level" of the campaign, arbitrarily set by the GM but defaulting to 10. This "level" also caps certain powers, notably attacks; for example at Level 10 you can only have up to 10 levels of Power Blast (or whatever it's called ... again, no books handy.) You buy everything with points: basic stats (often well past 18), feats, skill ranks, superpowers, super-gadgets ... anything and everything that defines your character. As with other point-buy systems, you can also sell down your stats or take on Weaknesses (is that the term?) that can hamper you at critical points.
True20 characters use point-buy for their basic stats (which, in a departure from d20 are in the range -4 to +4 or more ... think of the stat bonuses attached to d20 stats in the usual 3-18 range). Then they pick a "role": Adepts may choose a supernatural Power instead of a Feat, Experts have extra skill ranks and one better-than-average save of their choice, and Warriors have the best BAB and decent saves. Each role also has access to role-specific Feats. At each level, a character may acquire a different role freely -- essentially, multiclassing -- with BAB, saves, and skills accruing from the levels in each role.
Both use the Toughness mechanic instead of hit points, and both borrow heavily from the d20 combat system and other rules. M&M is way more flexible, but the complexity might be daunting at first. True20 is simpler for "typical" RPG worlds, but can be constraining if you're not doing typical Fantasy/Scifi/Horror with human-scale characters or find level-advancement constraining.