i have a few complaints of my own.
First off: i think the stage builder seems kinda last-minute. there's too few pieces, even w/ all the unlockables, and only 3 arbitrary backgrounds. i do like the fact that u can use all the songs you've unlocked though.
2nd: the online. ive heard several claims that it runs super smooth, but acording to my first-hand experience, these seem to be false. ive had some smooth games, ill admit, but sometimes the lag is so bad the game runs at about 3 frames per minute! and in lesser cases there is a split-second delay between when i press a button and when my character (Kirby, greatest fighter of all time) attacks. it is more frustrating then the enormous lag problem. and the whole anonymity of the public multiplayer seems like a pathetic way to eliminate online flamming, but it also eliminates the whole concept of online play! the ppl have no name displayed, no communication, its practically like playing w/ a bunch of lvl 9 comps (or lvl 3, depneding on the other players' skills).
finally: tripping or slipping. i think it is completely useless and stupid. what is it? why? it is a sad gameplay feature with no place in this or any other game besides maybe "Slippy: Adventures on Oil Slick Island."
i guess in a desperate attempt to make this game more than SSBM w/ more characters an better graphics, they added this and other ridiculous elements like stickers and the stage builder. but thats fine! im ok w/ them making it the same game w/ more characters, items, and better graphics; thats what a sequel is!!! Call of Duty 4 is the same as CoD 1 but w/ better graphics, new "stages," new characters, and new weapons. and thats what ppl want: more of the same tried and true gameplay, spiced up w/ better graphics, and characters and so on and so forth.
anyway, these are just a blip on the radar compared to all the great things about SSBB. i love it and i hope they keep making new ones, maybe w/ even more 3rd-party characters like Master Chief or Obi-Wan Kenobi.