For a game that hasn't changed much since the '80s, this version holds up very well.
If you still haven't played Tetris somehow, the goal of the game is to line up falling blocks of various shapes in a grid. When you make a complete horizontal line of blocks, that line disappears. As you complete more lines, the blocks begin to fall faster. When your stack of blocks hits the top of the screen, it's game over.
This is the same Tetris formula that's been used since forever, but if you haven't played Tetris since the Game Boy days there are a few new additions. The game now shows you the next 5 blocks you'll be getting instead of just the next one, and you can save a block for later by pressing the A button on the Wii remote. It will be put in a box at the top of the screen marked "Hold," and whichever block is falling will be swapped with it the next time you press A. Blocks also won't lock down immediately upon landing, and can be rotated for a few seconds before they lock, making faster levels more bearable for less experienced players.
I've found that Tetris plays much better on Wii than other current-gen consoles. I tried playing Tetris Splash on Xbox 360, but the 360's D-pad didn't always register my moves properly, and trying to use the control stick just felt weird. The Wii's D-pad feels just right, however.
Aside from the classic Tetris format, there are several new formats to keep the game fresh. One new format gives you a silhouette in the background, and you have to line up the blocks to create that shape, trying to deviate as little as possible. Another has a small climber at the bottom of the screen, and the goal is to guide him to the checkpoints on the grid by building him a staircase of blocks. It's tricky at first to get used to using the blocks for something other than making lines, but once you get used to it it's a lot of fun.
Another included variant lets you play the game with a balance board instead of a controller. The piece is moved by shifting your weight left and right. Shifting forward or backward makes the piece fall faster, and squatting rotates it. It's fun at first, but squatting gets old after a while, and I found myself accidentally dropping pieces too fast because I was leaning inadvertently.
The game also includes multiplayer variants. Besides classic head-to-head matches, there's also a variant that adds Mario Kart-esque items into the mix. By clearing lines with item blocks in them, you'll get a random item that will either hinder your opponent or help you. Some items, like the climber, don't do much to affect which way the match is going, but others, like the attack that makes your opponent's blocks drop much faster or the one that aligns all your blocks to the left or right, can really turn the tide of battle. Other multiplayer variants include 2-player co-op, where the grid is much wider and each player controls a falling block, and Duel Spaces, where players take turns dropping blocks, trying to close off spaces.
Head-to-head play is also available online, with or without items. While it's nice to see a rating system implemented, 6-player online is only for games with items. If you play without items, you're limited to 1 on 1 play. Item games are fun, but it seems to take the matchmaking system a long time to find more than one or two opponents to play with. The good news is that if all players agree, you can start with what you have so far, but if one person wants to wait, the whole party has to wait. There is a 60-second clock on game starts so that one player can't hold off forever and ruin it for everyone, but the clock resets every time a new player enters the party, so if someone is insisting on a full 6-player match, you could be waiting a while. Fortunately, the game developers noticed this and let you play in practice mode while you're waiting (or once you've been eliminated), but it's still a lot of waiting.
Overall, this is an exceptionally good version of a classic puzzle game. While the $12 price may seem a bit high for a game as old and simple as Tetris, there are enough game variants to warrant that price, and any Tetris fan, or puzzle fan in general, should give this game a try.