OK... The pdf of DC Adventures just came out, containing the M&M 3e rules. There's an awful lot to absorb. There's a lot to like in the new rules, some things seem weird or 'off' and I'll have to try them, some things are like, 'what were they thinking?'. About par for the course for a new edition.
I'll try to hit the highlights that would probably be relevant to True20. (There are some major changes to the powers, for example, but that's not as relevant.)
They've cleaned up circumstantial modifiers quite a lot. Now almost everything gives +/-2 or +/-5. There are some exceptions.
The tradeoff feats like Defensive Attack are now combat maneuvers that anyone can do up to +2/-2. The feats let you increase that to +5/-5.
'Taking 10' is now called a 'routine check', and is pushed a little harder in the rules. 'Taking 20' seems to have disappeared.
Every 5 points by which you make a check is called a 'degree of success', while every 5 you miss one by is called a 'degree of failure'. (Barely making/failing it is the first degree.) These are used A LOT in the rules. There's lots of stuff that says, "If you have more than one degree of failure, this bad thing happens," or, "If you get two degrees of success, this nice thing happens." I find this much more appealing than "If you make the check by 10" - it's more intuitive somehow.
Example: If you succeed in demoralizing someone with Intimidation, they get -2 to all checks for the next round; but if you have 4 degrees of success (make it by 15), they're at -5 instead. (Batman does not have much of a problem doing this to thugs. :)
Skills have, as mentioned, been greatly compressed. Usually it's just a matter of taking two old skills and sticking them together, but there are exceptions. Expertise is player-defined and covers anything about a subject not explicitly covered by other skills. So it can act like Knowledge or Profession, or in some cases even like Perform and some types of Craft. (Other types of Craft are now under Technology.) The GM sets the difficulties, much like Knowledge now - narrower Expertises should get a break in the difficulties compared to broader ones.
Persuasion (what used to be Diplomacy) has been nerfed a bit. The base difficulty to change someone's attitude is 15. For every two degrees of success you get, you can change it by an extra step. So far, not too different, though you don't need the table any more. Here's the catch: If you succeed and then try again, you still have to roll vs. the *original* attitude to improve it even more. And if you screw up, they not only revert back to their original attitude, they go down one from there! However, there is STILL no way for an NPC to defend against having their attitude changed. Sigh.
The Investigation skill, in addition to letting you find and analyze clues and set up surveillance, includes the old Search and Gather Information.
There's a lot of other minor changes to skills, I'm not going to try to list them all. Ditto for advantages ('feats').
Conditions have been cleaned up. There's a smallish list of 'basic' conditions, and more complex ones are built out of the basic ones. So 'incapacitated' is built out of 'defenseless', 'stunned', and 'unaware'.
Complications (basically Virtue and Vice) are pushed much harder in the rules now. They are a major component of the game, and everyone is required to have at least two. (And you'll probably want more, as they are the major way of gaining hero points - ie, Conviction.) As in 2e, the GM can also spring temporary Complications on you - having something bad happen but giving you a hero point for it.
Damage and Recovery have changed mightily. Bear in mind that M&M has always been different from True20 in this regard, to better reflect the superhero genre. (For example, True20 has an extra level of 'Wounded', which doesn't exist in any edition of M&M at all.)
In the new rules, there is no distinction between lethal and nonlethal damage. If you fail Toughness, you take -1 to damage. Two degrees of failure means you're 'dazed'. (NOT 'stunned'! So no more "stun lock".) Three degrees means you're 'staggered'. Four means you're 'incapacitated' - pretty much out of the fight. An incapacitated character who takes more damage moves to 'dying'. This is the only way for the 'dying' condition to occur from damage, so basically death will happen only if someone deliberately attacks an unconscious character. (Dying can also happen by Weakening someone's Stamina. "Draining their Constitution" in the older terminology. So, poisons, diseases, and weird powers can kill by doing that.) One stabilizes from dying in more or less the same way one does now, except the difficulty is 15.
If you do decide to attack a downed character, you can make a routine attack check against their 0 defenses - it's like shooting fish in a barrel. If you choose not to take the routine check, any hit is treated as critical. Oh, and critical hits have more options now. Instead of doing more damage, you can either add a minor effect, or substitute a larger one for the damage. So if you get a critical in combat, you can try to, say, temporarily blind the other guy. (The old 'sand in the eyes' trick.)
Recovery... Basically, you recover your worst damage condition each minute. (Each -1 is treated as a separate condition.) You can also take a standard action to Recover once per conflict to recover immediately, and you can spend a hero point to get rid of certain conditions instantly, as before. Regeneration speeds up recovery, while the Healing power causes you to recover with success, and heals an extra condition for each degree of success.
So what about long-lasting effects from damage? Those are Complications. The GM can say, "So you fell off the cliff and got incapacitated? You broke your arm. Take a hero point." Until it heals (basically when you and the GM feel it's time), every time that broken arm causes you a serious problem, you get another hero point. (The GM could explicitly define what effect the broken arm has, or he could just wing it.) So, lasting damage is purely dramatic in nature - I quite like this.
There are some optional rules given to make combat somewhat more lethal, and no doubt these would come standard for the typical True20 game. Basically the 'dying' condition can be added back to the Toughness chart in the event of attacks that are deemed lethal.
There are quite a lot of changes to combat actions and maneuvers - they've been cleaned up considerably. I haven't really digested the changes yet, but one that really stood out is the new 'Defend' action. If you use your standard action in a round purely on defending yourself, your defenses become *active* - the attacker has to make an opposed check vs. your defense. AND your defense roll is treated as if you had rerolled it with a hero point/Conviction! So your roll is automatically between 11 and 20.