Just completed this having only started after lunch, really good game IMO and a lot better than I was expecting. I'd definitely recommend it to anyone who likes casual FPS, in fact I'd say it's one of the best FPS games I've played in a while.
+Decent graphics
+Consistent i.e. doesn't take itself too seriously
+Skillshots are MUCH better than the achievements you get in most games, because they actually have a meaningful benefit in the game (skillpoints), so I actually felt like I had an incentive to go for them
+Good fun, what's not to like about pulling some dude towards you and then kicking him onto a catcus? Should feel gimmicky but because the game is actually built around the mechanics rather than them just being tacked on at the end, it works really well.
+Decent performance, 60-120fps.
+Decent boss fights for the most part
+Very good value at £3.75
-Campaign maybe a tad short at 7hrs
-Gets a bit annoying at times when it comes into interactive cutscene mode and you can't run
-Could have used a wider variety of baddies
-Don't get to a have a proper fight with the final boss just Simon Says stuff
-Teammates don't seem overly effective, in cutscenes they can one-shot the enemy from half a mile a way, but in standard combat they seem to just be firing water pistols
-Did get a glitch on the final level where I had to reload the last checkpoint because a wave of enemies didn't get triggered for some reason so my teammate was trying to hack a door for minutes with nothing happening.
All in all a very good modern take on Painkiller, apparently BS2 has been canned which is a shame IMO.
there is an "official" thread.