Dragonball Z Budokai Tenkachi 2

[JKTrix]

Get a Wii. Play it on the Wii. You WILL love it. This game is freakin' awesome.

And they always need to leave room for improvement, so they did leave some things out that they probably could have.

I don't know how the story mode could be "better". Perhaps if it had the awesome cutscenes of the first Budokai game, but think about what you actually have in Tenkaichi 2. Tenkaichi 2 goes through the ENTIRE DBZ storyline, including the movies, and even includes alternate stories and elements from Dragon Ball and GT. The box claims 'over 120 characters', which is a bit dubious since a good chunk of them are transformations of existing characters, but its quite true. Every stage of a character has a different move set, so they are essentially a different character. Kid Gohan plays different than Teen Gohan, Sword Trunks plays different Super Saiyan Sword Trunks, who plays different than just-plain-no-sword-Trunks, The Great Saiyaman plays different than Normal Adult Gohan who plays different than Super Saiyan 2 Adult Gohan...

The amazing amount of content in this game more than makes up for whatever flair the story mode lacks.

Now for your points:
1) I hope you mean the Japanese soundtrack, the US one isn't that inspiring. Some of the music pieces in this game are actually quite good, and fitting for an action/fighting game.
2) Bigger stages wouldn't hurt. Might need a more powerful game system though. If you didn't notice, the stages are completely destructible, even without world-destroying skills like the spirit bombs.
3) More characters wouldn't hurt at all
4) Spoke about story earlier
5) Did Teen Gohan ever wear a uniform like Goku's? We only see him in Piccolo's if I recall correctly. Adult Gohan's Orange Gi is un Ultimate Gohan mode. Also, did you notice the difference between the first few changes of Goku's costume? All that changes is the symbol on his gi, reflecting the different people who he's trained with (Roshi, King Kai, etc). Yeah, I'm a DBZ nerd.
6) Well, stages aren't that big. If you are near a mountain when you smash them and you aim the shot correctly (you did know you can aim your smashes, right?) then they will shoot through mountains. The main point of smashing someone like that is to immediately follow up with a Blast 2/ultimate technique, or go in for the Dragon Homing/Vanish Attack combos. Try it out, it's verrrry fulfilling. (Maybe less so on the PS2, Wii version is freakin' awesome.)
7) I assume you mean in Story Mode. Go through Story Mode as a lv 8 character (no bonuses) and see how much longer the fights last.
8) If the superstrong characters were so blatantly overpowering compared to the likes of earlier/weaker characters, the game balance would be abysmal (like in Tenkaichi 1). If everybody is playing as the Super Saiyans because everyone else is useless, the game will get very stale real quick. Having the 'weaker characters' being able to stand up at least a little better balances the game a bit more. They are still at a disadvantage though. Unless they are all pumped up on the stat bonuses, then yeah they would be harder to beat.

No doubt the Budokai series will continue, whether or not it'll continue in the 'Tenkaichi' vein remains to be seen. But there is always room for improvement.

Like I mentioned at the beginning, if you can get a Wii, spend time learning how to play it again with the Wii controls. It is amazing.