I've only had time to play a few levels of CE and a couple of H2, but in either case I've had no problems. The unified UI for the terminals I commented on elsewhere, and while sort of annoying in process, it wasn't buggy.
The only bug-like annoyance I had so far was at the flood appearance in CE; the sounds were odd. The spore and weapon sound volumes were just wrong (silent spores, however, are in a way a little more creepy!)

That's it so far though.