He and his brother (soon 4 years) have a fantastic kind of cooperation around the game, where the older orders/asks (we try to make him ask politely) the eager younger to place relevant Skylander character on the "portal" (in order to open gates and fight certain mobs etc).
It's interesting to hear, and watch. We've been coaching younger brother to play a little, but he tends to choose to watch his brother for the time being. Younger prefers to play games on the iPad.
Gameplay is rather "nice", sure enough you figth/kill opponents, but it's not quite as obvious and graphic as it could be. You select your figurine, place it on the "portal" and the character you chose is magically entering the game. We have the Wii version and the controller gives some feedback on entry (and certain other actions).
I actually like the figurines so much I bought my own last night - "Ninjini" featured on the photo above. :-D