I want to start off on a positive. It should be noted that Nintendo and a small handful of developers put out some very killer apps for the Wii. Barring Wii Music, everything Nintendo has released themselves so far is gold and much of their efforts still rank high on the NPDs. The same cannot be said for good 3rd party games however. Efforts like Madworld and Dead Space have notoriously poor sales, despite the quality of the games themselves.

The Wii is Nintendo's newest console system and works with a 2 pronged input system. There is the wii-mote which does the majority of the heavy lifting and an attachment of some sort, which is usually the nunchuck. You play by pointing the wiimote at the screen to move the sensor, though some games have you turn it sideways in throwback to classic Nintendo controllers. if you want to play multiplayer games, you have to buy another controller and another nunchuck. The system allows up to 4 players and so it can get pretty pricy. If you want 1:1 controll, you must buy an additional addon, the Wi Motion Plus, though it only supports a handful of games currently.

The problems with the Wii are as follows.
1) 3rd party support. There are a lot of 3rd party games on the system. However, to call most of them fun or functional rather than appalling abortions of game design is kind of a stretch.
2) Motion control. Depending on who makes the game, the control itself can be a bit dodgy. If Nintendo makes the game, strap in because you are in for a very enjoyable ride. For the other developers trying to make a buck on the flood of shovelware, not so much.
3) Motion control. Yeah, I already listed this but there is another issue. For the first few days playing with the system, it is a LOT of fun. But after a while, you get sick of having to waggle around and look like a fool playing your games. After a hard day at work, sometimes you just want to sit down and relax to a good game. This is likely a problem with the fact that multiple generations now have grown up with standard controller input for games and that is what we are used to. It is also the case that sometimes adding motion control for the sake of motion control is just not that compelling.
4) Lack of high definition. Sure, you can get composite cables and bump it to 480p, but when you put any of the games next to a 360 or PS3 game, the flaws are apparent. If the gameplay is good enough, slightly inferior graphics can be easily overlooked. See Mario Galaxy and Metroid Prime 3, for examples of this. But, most of the games look subpar even by late-last-gen standards, and on an LCD big screen this just gets magnified, literally.
5) Slowness pt 1: SD. The Wii only comes with 512MB of internal storage. This fills up rather quickly, but can be supplimented with an SD memory card. However, moving things too and from the card can be a bit frusterating. It is a great addition to the system given that SD is dirty cheap right now, but the speed issue remains. Add this to the fact that being able to play games directly from the card wasn't added until last summer and you can see that SD wasn't a priority.
6) Speed pt 2: Network. The Wii has an internal Wifi antenna, which is great considering that to get one for the 360 you must buy a proprietary antenna, which is pricy. However, the speed is ...molassas-esque. It should not take a minute or more to download an old NES/SNES game. The file size is not that big. System updates shouldn't take as long as they do. And if you have tried watching Nintendos sub-youtube quality streamable video... You can buy a usb ethernet dongle to help out, but it is bottlenecked through USB, so while it is a speed boost, it isn't a huge one.

It seems as if I hate the system, and I guess to an extent this is true, but not entirely. I would just say that for the first time in my life, I am not their target audience. This generation, Nintendo more or less snubbed their core long term audience in favor of the new and burgeoning casual market. That is within their right as a company and it has helped them become the frontrunner of this generation in terms of sales. It is an easy pick up and play system for people who might not think of themselves as gamers, and those peoples parents. Killer apps like Wii-fit allow people a fun way to lose weight and keep track of their progress. It is great for parties because the majority of games seem to be mini-game compilation, so there is a very pass the controller/competitive vibe to the whole thing. But, for those of us who just want to play fun games, sit back and relax, it just isn't there the majority of the time. It's success almost makes me sad, because when NIntendo goes to create its next generation effort, it will move in a similar direction, reinforced by the sales and novelty of the wii.

I was one of those gamers who was chomping at the bit for this system and bought one day one. I don't totally regret it because I got some use out of it for a while and it is cheaper than the other systems. However, I find myself wanting to offload it on someone else, as it sits covered and dust, a reminder of the promise it once held but didn't QUITE deliver upon.