Damn. I may have to take back my former statements. Either that, or this boss fight is just fundamentally fucking broken. Giant tentacle monster... the pattern is easy enough to figure out, it's fairly simple. Shoot the glowing bits when they try to attack you. But my shots don't register half the time. It's like you have to intentionally aim slightly off, but that doesn't necessarily get you anything. Sometimes the hits register, but by and large I can't make it consistent, and there's so much fucking camera jiggle that it's near impossible with the controller. I suspect it wouldn't be that much better with a Move controller, though, as even when I'm aimed spot on, it just doesn't work. Plus there are times when you need to use stasis to get through something and it doesn't register that you did, and you just stand there getting hit like a fucking dolt even though you did what you were supposed to.
I'm horribly disappointed because I was really having fun with this game, but at this point, I don't think I'll be able to move on from this level unless I set the difficulty to easy and throw myself at it 12 dozen more times, which I'm not even remotely interested in doing. I don't know if this was a problem with the original version or just the port (Pyro, you played it... thoughts?), but I'm really fucking disappointed, especially since the rest of the game has been very solid and enjoyable so far. I even went and read a FAQ to be positive... and sure enough, I'm doing everything right, the game is just messed up.
EDIT - Watched a video online, and the fight is definitely broken. It looks like if you bring the pulse gun and just stockpile ammo for it for the fight, the rapid-fire hail of bullets makes it a lot more likely that you'll hit the spots you need to. But even in the video the guy was getting direct hits that were doing nothing, and the stasis thing borked for him too. Dunno' how this got by QA. The rest of the game prior to this had felt very polished and balanced.