Here's my impressions from the Alpha..
For one, I'm shocked that they've released an Alpha of this. Bungie is no stranger to allowing Beta testing, but ALPHA? That's a bit extreme. They point out the fact that some stuff may not be completed. Well, it would be good if you'd say explicitly what that stuff is, like if a particular objective can't be filled or whatever.
Anyways, there's not TOO much to say about the game. It gives little to no story structure. Apparently though Earth is in shambles and space fighting is where it's at. Gameplay-wise, it feels like Halo... like to the point of almost insulting. I'm sure many of us expected the game to have at least some of the same shades, but this is... well I can't think of the right word. I mean hell, they even copied the shotgun look, animation, and sound from the Halo series. Check out this clip I recorded and tell me (people familiar with Halo) that you don't get at least a FEW flashbacks of the Flood..
When you're not fighting, you for some reason go into a 3rd person mode as you walk around I suppose hub-like towns, as seen here. I couldn't tell if I was playing Destiny or Mass Effect.
Still, the action and other gameplay is perfectly serviceable, so I guess I can't be too harsh, and again it is still an ALPHA. However, from what I've seen so far, I don't see this game making back all they money they're predicting it cost and required to recoup.