Communial experiences, player status and competition are powerful motivators. Motivations that can be captured through the internet, recording player records on servers and connecting players across the world. Combining this with fun-orientated gameplay - that has alot of potential!
Although, about this whole motivation thing - why am I so convieniently motivated to slay innocent people on GTA:SA!
On topic, didn't great games such as StarCraft, Fallout and UO utilise 2d isometric methods? I still play Doom and Wolfie-stein on occasion! I think 3d is great for marketing a product, creating an immersive atsmosphere and sparking that "wow factor" but it doesn't maintain the momentum without great gameplay and some games just don't need to be 3d...Snake3D, ugh!