Yeah, I have a similar feeling on this. I think the game is disappointing, for sure. I would have loved to see more planets, the mission variety is pathetic, the end is a huge let-down, only having 4 PvP modes is baffling coming from Bungie, the patrol missions are blatant filler, and the lack of easy access to voice chat is frustrating.
But the actual core gameplay is still awesome. Punching dregs feels great, speeding around the moon is gorgeous, enemies die in just the right number of hits, the class abilities feel substantial and powerful. I'm compelled to get my gear up at least to the point in which I'm able to clear out the first raid. That'll determine whether or not I'm going to drop some money on an expansion.