Still one of my favorite Superhero RPGs, alongside Mutants and Masterminds; If you want a class-based approach with a good handle on creation, this is a good system. It is extra-worth it for being "Stingy Gamer," which makes it less expensive by removing the color.
Overall, the system works similar to Champions' point-based system (point-based seems to work best in Superhero gaming) with normal XP awards giving the character bonus depending on their "class," advancing in a method similar to regular D20. This can be difficult at times (the PowerHouse class seems well overpowered) as the classes don't always correspond well to the direction your character wants to take. However, you can forgo the class-based advancement and simply give out 10 XP per level benchmark (which is about what the design supposedly works out to).
Overall, a good book, lots of good history on Comics and trends, including an explanation as to why its the "Silver Age" Sentinels (which personally, I find resonates well as a longtime comic fan), lots of great info on the history and environs of the world. It has full writeups for its signature heroes (which M&M does NOT have - it has "second-stringers"), as well as several of the signature villains (which M&M does also have).
Plus, if you like Champions, they did have a cross-over book which you can use.
[4 of 5 Stars!]