Great looking game, unfortunately I was flying solo in the world so I could not appreciate the "MMO" feel of the game.
Collecting the stamps was fun, but the speed of the plane is way too high to appreciate the stamps themselves. Perhaps having some sort of bullet time slowdown on pickup to show off the stamp for a second or 2 would be nice. Also the fuel tanks can be hard to distinguish from just a normal building when they are on the world map.
Overall fun and great looking game. Well done !