I finally got a chance to play this for about an hour last night, and I can't say that I'm terribly impressed so far. I did a handful of the missions, which felt very much like Borderlands (as mentioned many times in here). The problem is that the missions were rather boring and didn't seem to serve much purpose. They all seemed to be "go find this guy or this object." Rinse and repeat.
I know that running in mud is a common complaint against Halo, but it seemed even worse here. And I hate clicking the left analogue stick to run. Very awkward.
In terms of graphics, this feels like a last-gen game with a resolution bump. Regarding audio, I recognized many of the sounds effects pulled straight from the Halo bucket.
I didn't get a chance to play MP and I never ran into any random players during the missions, so maybe there is some depth there that I didn't get to experience. Obviously this is just an Alpha, but as far as first impressions go I really didn't get sucked into the game like I was hoping I would.