A shit TV is gonna have pretty mediocre display settings, such as blaring contrast, wonky light/black levels, pretty bad sound quality, no real customization options (so good luck trying to fix these problems by adjusting settings), and a few other problems. Monitors suffer from this same problem, but the price difference between a nice monitor and one that's shit but cheap is a smaller difference than once you get into large TVs. For example, my housemate saved $150 on a 42-inch display by going with a cheaper brand. He regrets ever doing so for the reasons stated above.
What DCG mentioned above you is a VERY big thing to consider if you're going to be gaming. Unfixable lighting levels is not something you should want to deal with.
Personally, I've also had bad experiences with HDMI outputs from a videocard to a TV. Often the image looks like it was JPEG'd and has very strange lighting distortions that it otherwise wouldn't have with a straight DVI connection. Alongside that, the TV would often force me to run at a much lower resolution in order to even recognize the HDMI, where you would then have to use your videocard to rescale the image back up... which creates even worse artifacting.
If you want a simple solution without much thought, and you don't care about the repercussions, a TV is a good decision, especially if you'll be using it for much (MUCH) more than gaming, as in, gaming/computer is not the main thing this display would be used for. If you plan on gaming and using the display for computer activity, for extended amounts of time and as a main source of entertainment, you're much better off getting a nice monitor.
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