I really didn't like the idea of this product at first. Take Mutants and Masterminds past the PL20 barrior into "Cosmic" levels? Sounds like a munchkin power gamer's dream.
But I was wrong.
I'm still not convinced about PL20+ play being balanced, but this book goes a long way towards addressing issues faced at that level. But even if you don't plan to play at those levels, there's plenty of material here that you could use at PL10-20.
About half the book is colour and background, describing the issues faced by cosmic level heroes both in terms of gameworld and game mechanics. There's 101 scenario ideas, many of which could be adapted to world-class heroes.
There are the usual crunchy bits - new feats, many of which may be usable by villains at the PL15-20 range. and DCs for using powers at ultra-high levels (cure cancer? DC60 Scienc e check please.)
The sample cosmic level characters have some interesting ideas, and could probably be adapted as lower-level characters, or major villains for lower-level teams.
Then there's the mass battle rules - simply put they boil down to grouping larger numbers of identical combatants into a single "metacharacter" and fighting the combat normally using an extended timeframe, based on the power of the character. This is more of an abstract resolution system, but I think it would work well. Definitely a must if you want to refight the Terminus invasion, but you might also be able to use this for those Agents of AEGIS vs Hordes of villain minions battles that go on in the background while the main heroes duke it out.
What's bad? The artwork, while nicely done, isn't in the usual comic book style, and one or two don't seem entirely appropriate to the issue of "cosmic" heroes. Didn't work for me (with the exception of the pic on P74), but YMMV.
The layout is crisp and clear, and there are two versions, one with borders for screen viewing, one without for ink-friendly printing.
Is this a must-buy for M&M GMs? No, not buy a long shot. But it certainly is a worthwhile purchase.