the magic of Smash imo is if you want to just have fun with it you can, no need to learn a ton of combos or strategies, you can just pick up and play and have a blast! You can customize the hell out of the game and do so much with it. At the same time, if you want to go at it like a street fighter with combos and strategies and such, it gets pretty damn deep. Its all on how you want to do it and its enjoyable regardless. My friends and I play Brawl hardcore and can say that there is nothing shallow about this game. Yeah it has a kiddy pool, but it also has a diving board at the far end where far deeper waters await.
Im not sure how PSAS is as Ive only read about it so far, does it include the same level of customization as Brawl? Is it as pick up and play?
it certainly has the pick-up-and-playablility of smash. each character has basically 12 moves as illustrated by each combination of (square, triangle, circle) + (up, down, forward, or don't press the analog stick). add to that a jump, block, taunt, and super (aka smash) button and you are good to go. some of the moves are chargable too.
some characters (like kratos) is really, really easy to play just by button mashing. but there are others which are far more complex. sackboy kind of plays like olimar in that they are both "utiltiy" characters. toro plays a bit like shiek/zelda in that torro has three costumes each with unique move sets. harder to play but also really versatile once you master them.
things get even deeper if you want to learn which moves will combo together. you'll need to know that if you want to be amazing at this game but certainly not needed for beginers.
really, it plays like smash but with less character cloning. PSAS as 19 very unique fighters. SSB starts with 35 but cloning means there are really only 28ish unique fighters. more, but not as much more at first glance.
games can be customized too. time limit play or stock play, team battles or free for alls, pick which items will or will not appear, AP modifiers (same as brawls damage modifier), minimum AP levels. it's been a while since i played smash but i don't think PSAS was missing any features there.
if all you want to do is play multiplayer brawls with your friends you won't feel like PSAS is missing a thing. it's really the solo campain where SSB is really outshining PSAS.