The formula is all there, but it'd go a long way to improving the game if the AI were more... Intelligent I suppose. For an alpha, their behaviors are mostly passable. However, I never feel like they can kill me until I'm overwhelmed by them, and it's at that point where their large health bars completely overshadow any tactics they have. A high level enemy running up to me isn't a challenging opponent; it's a wall that absorbs bullets. Similarly, the bosses themselves only appear challenging because the grunts on the ground detach our focus from them. I've only died fighting Sepkis because the Captains will bottleneck me into the hallway we came from.
The Hive knight is probably the enemy I like fighting the most, because it uses cover and it regenerates its health if you shoot when its shield is up. The other ones either stand still or blindly rush you and don't offer much combat wise.
There are many clear improvements to be made balance-wise, but I hope the issue with Destiny's combat isn't so inherent that it wont be possible to improve.