Having just finished it, here are my thoughts... I had very few serious framerate issues while playing. There were a few minor things, especially while driving, but none that really impacted my ability to control myself or fight. I had expected more in battle but didn't really have that much even with a lot of action on screen. I mean don't expect Halo framerates, but the action isn't as fast paced so it works out fine.
I had a couple texture issues but only a couple times and they were gone next time I loaded. Didn't have any popup issues and I never got stuck in an object (don't think I even saw the CPU do that).
AI teammates had the occasional issue getting stuck behind something while following me, but that was pretty rare. You sometimes have to be careful not to be in their line of fire, but that was easily manageable. Enemy AI isn't great, but I doubt a patch will come to really fix that.
Overall I definitely say buy it now. Well worth playing as it is now.
I'm only a small ways in and I agree, the bugs aren't nearly as detrimental to the experience as I was expecting, and obviously issues with the gameplay mechanics themselves aren't something that will be fixed in a patch.