Budokai Tenkaichi strikes out from the previous series formula and actually ends up being a whole lot of fun.
Gameplay - Change is good. Not only does this game do away with the previous Budokai's typical side-by-side fighting, it makes the battles totally free roam. Really awesome to say the least although Budokai fans might feel turned off by it. Also, the game has TONS of DBZ characters for you to pick from ranging from series standards like Goku and Piccolo to more minor fighters like Jeice and Bardock. An unfortunate feature left out from the first series is the ability to transform in battle.
Graphics - Pretty much the same cel-shaded goodness the previous Budokais offered and the effects of everything from the special moves to the exploding scenery during battle look sweet.
Sound - You get the option to choose between both Japanese and English voices which is a huge plus. All the sounds, music and voice acting are pretty standard although the game unfortunately rehashes a lot of previous music.
Replay Value - If you got a friend or sibling who's a fellow DBZ nut, you two will more than likely be playing multiplayer together for quite awhile (CPU opponents are also decent to fight against as well). Also, there's a surprisingly huge amount of unlockable content (usually in the form of new characters).
Bottom line, if you are even remotely a fan of DBZ, you should check out Tenkaichi. While it differs greatly from the previous series' elements, its own take on the DBZ universe ends up being quite a lot of fun.