Offense: C. I think Sonic's offense has it's ups and downs. In some cases, offense can be phenomenal (speed, ASC, tilts, etc), and it other cases, his offense sucks (killing power, range, priority). It's one of those things where if your opponent has no idea what Sonic can do, you have a mental advantage, but if he/she does, you got a nice little problem on your hands.
Defense: B-. Sonic's defense is not just in his shielding or his spot dodging, but in using the spring jump to escape combos and even running away. Most of the time, I end up playing the whole "defend and punish" game with Sonic, but at the same time, punishing with Sonic's smashes (my particular natural instinct) has a hi chance of failure because of the pre-lag. His defense is very solid, and in theory, you shouldn't get hit with Sonic, but...
Recovery: A+. When you know what you are doing, there is absolutely no reason you should not recover from anything that doesn't knock you out immediately. Between the spring jump, the homing attack, the spin dash, and the spin shot, you shouldn't not make it back to the stage. Even if someone decides they want to edgeguard, a well placed fair or homing attack will allow you to defend yourself and then hit a spring jump with no problem. I can honestly say that Sonic has one of the best recovery amongst the two jump characters. I never worry when I'm off stage.
On Stage Game: C? I'm not exactly sure what this means... if it means a combination of your offense and defense, it's a C. If it's your aerial game onstage, I'll give it a C as well, because while Sonic's aerials are good, some of them lack the priority necessary to make them tops.
Off Stage Game: B+. Only because I don't fully utilize the gimp game the way I should, because if I did, I'd probably give it an A. Sonic's off stage pressure game is frikin incredible, but at low percents, I tend to have this fear that I'm gonna get countered for some reason, so I don't do it. At higher percents, the opponent got this panic feeling about them, so it turns into a different off stage battle.
Combos: B. Sonic can go in with the combos. From my knowledge, Sonic has utilt, dtilt, fthrow, and uthrow to set up combos, plus dthrow to tech chase, which isn't a combo, but this is brawl, so you gotta work with what you got. In the right hands, Sonic can rack up plenty of damage without the opponent knowing what the hell happened... but if only he had death combos...
Overall: C+. I like Sonic and I like how he plays. It's different, kinda complicated to fully implement everything, but he's very effective at everything except non-gimping kills. Even though the rest of the world hates him, Sonic's a pretty solid character, unlike some others...