That depends entirely on the game.
The likes of Tumble, Heavy Rain, Flight Controller HD and a few of the Sports Champion games require very little room.
Two player table tennis however (Sports Champions) requires quite a bit of room, but is a great game.
Owning a Wii I have to say that Move outperforms it to a huge degree, far more that I had originally believed it would.
Small movements are far more accurate (even in comparing to the Wii Motion+), however its also the ability to handle movement on the Z axis that is the biggest difference.
The Wii really doesn't do that side of things well at all (movement towards and away from the screen), however Move deals with it stunningly well and it does make a big difference. Its something that Sports Champions Archery shows off well. As you move two controllers away from each other, the distance is used to provide the draw strength of the bow and therefore the power of the shot.
The ability to use two controllers together (and not have them linked by a wire) also opens up a lot of options as well.
You have to synch them up just like the normal controllers, but in the same way its a one shot deal. Just plug in the charge lead (same one as the Dual Shock) and its done.
You do have to calibrate the move controller for most games, but that takes a second, and is worth the tiny amount of effort for the accuracy you get.
Regards
Scaff