You clearly need to stop playing it as a proper fighter then, I consider it a beat-em-up (pretty much has the same kind of mechanics. Beat the snot out of dozens of characters, only one combo, etc.)
It's a lot more fun than you apparently think, I have no problems with the one combo, no ingame transformations, or any of the other stuff people have problems with. What I do have problems is how bad the release is, currently for me the cutscenes play in slow motion, except the sound is fine (The voices at least, all other sounds are desynced like crazy), and the opening has lag spikes. These are proper reasons to dislike the game.
It's not the best DBZ game, but worst? No way, it's no where near the worst, you clearly didn't play DBZ Taiketsu on the Game Boy Advance. And I'm one who always tries to find good things in games, I happened to like Burst Limit, Super Dragonball Z, and even Ultimate Tenkaichi (.....in short bursts at least).
Again, you're being way too hard on this game. But hey, just my opinion, feel free to ignore it if you so wish.