I bought my Sentra as an economical commuter car for my 116 mile daily round trip to DC. The car has better power than I expected from a 1.8L, has decent road manners, acceptable ride comfort, and when driven properly can get very close to the EPA estimated 34 mpg on the highway. My actual mileage usually comes in around 31-32, but I do tend to have a heavy right foot. My only real complaint, and this is a common trait in every Nissan I've owned/driven, is the interior room, especially in the rear seat area. I'm 6'-3", and could use just a tad more leg room in front, but I wouldn't even consider climbing in the back of this car. At 23k miles reliability has been perfect so far.
Peppy engine (for an economy car), sporty styling, good handling (again, for an econo car), good a/c.
More interior room (which I believe they've addressed for 2007), maybe a little better base sound system.