Still waiting for Tetris Attack? Well, technically you don't have to wait any longer - Puzzle League is basically the same game with a different name.
Tetris Attack, the SNES game, was a Westernized version of the Japanese game Panel de Pon, which starred its own cute cartoon characters. Tetris Attack removed all of these and replaced them with characters and enemies from Super Mario World 2: Yoshi's Island. This game is the first "Puzzle League" game, and uses characters from the Pokemon anime. Two more Puzzle Leagues have followed so far (For GBA and DS), but these aren't based on any other game.
Pokemon Puzzle League is another block puzzler, but here the blocks slowly rise up from the bottom of the screen (if you're really good and want to speed it up, you can command a number of rows to rise up at your will). The game is more like Columns than Tetris, as the objective is to line up a row or column of three identical blocks.
Because the blocks appear on their own, you can't turn or move them in mid-air or anything like that - instead, you can switch the position of two blocks next to each other with a cursor you can move across the playing field. You cannot swap two blocks above each other, however, and if you move a block over a ledge it will drop down.
If you can string together a combo, a large coloured block will be dropped in the opponent's field, sort of similar to Puyo Puyo's garbage beans. If you make a small block that touches the large block disappear, the large block will turn into a whole bunch of small blocks for you to use (if the large block is big enough then it might also split into small blocks plus a slightly smaller large block). If the blocks reach the top of the playing field, you lose!
It's not like that's all you can do though - this game's got a ton of modes. There's a standard one player mode, where you try to keep going as long as possible and there is also a 3D mode here where you play on a field that looks sort of like a cylinder and the blocks wrap around!. There's also a one player mode where you play for two minutes and score as high as possible, and there are two story modes. In one, you basically go through the events of Pokemon Red/Blue/Yellow, battling the various gym leaders and Team Rocket. In the other, Team Rocket steals your Pokemon, and you must battle them numerous times in "challenge" levels, where you simply must get the blocks down under a certain line. In Puzzle University, you must clear a pre-made field within a limited number of moves. Of course, you can also play against a friend.
As stated, the game is based on the Pokemon anime. Aside from the obvious use of characters like Ash, Brock and Misty, this also means that, yes, the game has a ton of voice acting and music from the series and movies. However, this game was first released in 2000 - since then, all voice actors on the English show have been replaced. No worries though, the old voices have been kept in the game. There are also actual cutscenes which are similar to the show: quite a feat for the N64.
Overall, Pokemon Puzzle League is really just Panel de Pon/Tetris Attack with a Pokemon makeover. That's not bad though, because it's still the same game, and it still rocks.