One of the difficulties with superheroes as a genre is just how very open-ended it is. This middle chapter in the Aeon Universe Timeline manages to pull it off, however, by simultaneously providing a huge number of options for your by-the-book players/GMs while also granting a large number of jumping off points for players who want to craft their own hero to be their way.
I actually bought this as a supplement to my Adventure! game, and if you're buying it for that purpose then it's possible that you may be disappointed. The super-science feature, for instance, is no different (it is just as easy to invent a stat-enhancing drug in the early 2000s as it is in the mid 1920s, apparently.) While the book doesn't offer much in terms of base classes that Adventure! has, it does offer three prestige classes not found in Adventure!. Strangely, while the Vigilante and Crusader class left me a little wanting (I kind of wish that the Crusader's Trademark Attack gave you more than a +1 bonus), the class I found the most interesting was the Gladiator prestige class. Rather than an example of the broadest possible archetypes for heroes, the Gladiator is a more focused story idea.
Taken on its own merits, however, this book is astonishing, and allows you to do everything from subtle martial arts experts with a knack for using gadgets to planet-smashing tanks mutated well beyond the point of humanity. A definite buy that I wish had some more follow-up material than what already exists.
[5 of 5 Stars!]