I think it depends on the game (and to extend, genre).
In the GoldenEye days, split screen was the only option for multiplayer, so it was great FPS splitscreen fun. In today's era, it's not needed for certain games imo.
Split screen still works great for party games and things like Mario Kart, but I think most FPS fans want the whole screen for themselves (at the very least 2 player splitscreen... 4 player is simply too small, even on a huge screen).
of course this is just my opinion and personal taste.
oh the other hand, there are options if you must have split screen in high intensive graphic games. RainbowSix Vegas, for example, downgrades the graphics when playing in any multiplayer mode to keep the frame rate up. The graphics still look decent, just not as good as
