In Surface Tension the super human abilities of the grunts start to get annoying. They have instantaneous reaction time, perfect vision and incredible aim. It forces you to play the game in a way that isn't as fun. In the original I preferred playing on Hard because the grunts lived long enough to actually move around and do things, and that made the fights interesting. It wasn't just "see enemy, kill enemy, move on", you had to keep moving and switching weapons. But there's no room for that in BM (on Hard) because if an enemy sees you it's shooting you, and hitting you, ten out of ten times, so you can't afford to be in their line of sight and not killing them right away. It's something I really hope they address if they plan to patch the game.
Also, the grenade physics seem to be lifted from HL2 and I never liked it there. In HL1 I can throw a grenade exactly where I want it, every single time, but in BM they never go where I want them. It's a weird throw, and it has that HL2 issue of not coming out of the centre of your screen, so if you're peeking around a corner it's probably going to clip a wall. They're also not as powerful as they should be IMO, their impact radius needs to be a bit bigger.