I have played Champions as well, and HERO is really a great system.
Mutants & Masterminds incorporates some very similar ideas. You have character points, called power points (also levels (power levels in MM), but they are not nearly as limiting as in D&D, they just give you a limit on the number of power points, and a maximum level for each skill/power - similar to the Champions limits on active points, OCV/DCV, etc), powers that can be modified with advantages (extras) and disadvantages (flaws), but the system is a lot easier, as all those extras and flaws just change the cost per level by +/- 1, so not fractions to worry about, skills, feats (a mix of D&D feats, and stuff that's similar to HERO Talents/Perks and even some low-cost powers), and also weaknesses, which limit the character but give you extra points.
You have quite a bit of freedom, you can spend as many points on attributes, skills, feats, powers, etc as you like (and can afford), there is no level progression as in D&D, you just gain 15 power points per level and your rank limits are increased by one.
Also there are no hit points, which is very good. The damage system looks pretty cool. Whenever you get hurt, you make a damage save (like a fortitude save) and usually you just get a -1 towards any future damage saves (until rested), but if you roll too low, you get stunned or knocked out.
It really looks like a very well thought out system. And while it does not have the ultimate flexibility of the HERO system, it retains enough of it, but makes character building a lot easier.
I don't know any other d20 superhero game, but Mutants & Masterminds looks very good. The book (layout) is also done in a very cool style. You can't go wrong with that one.
Bye
Thanee