Although I said I was typing this on a 2 ms screen, I am probably getting three IPS panels for my new eyefinity setup. They're at 14 ms, and I've read somewhere that 16.7 ms is 1 fps in your game (trying to find the source all morning :~ )
Anyway, IPS panels are of much greater image quality, give much more contrast (also from color to color Haldi ;) ) so you will even see enemys lying in a dark corner, whereas on a TN panel you would just get slapped in the face by them. I've read some stuff about IPS panels 'tearing' when the screen must react to, for example, a strobe light in your game. However, turning on V-sync in the game options menu will dismiss this problem ( http://en.wikipedia.org/wiki/Screen_tearing ).
Input lag
Video games, which have a wide variety of rendering engines, tend to benefit well visually from vertical synchronization, as a rendering engine is normally expected to build each frame in real time, based on whatever the engine's variables specify at the moment a frame is requested. However, because vertical synchronization causes input lag, it interferes with the interactive nature of games, and particularly interferes with games which require precise timing or fast reaction times.
This is really the only thing that TN panels have over IPS panels, and I doubt that (unless you are a world class gamer) this will weigh up against the far more superiour quality of IPS panels.
Hope this helps!