So yeah. I didn't know until friggin XEN that you need to sneak around those tentacles, and not run around avoiding them. Frantically climbing ladders and smacking planks with your crowbar while muttering "Sh** sh** sh** hurry up hurry up F$%K ARGGGGGG" is very fun.
Blast Pit has to be the chapter I reloaded the most, due in large part to me not putting two and two together at ALL during that chapter. It took till I tried throwing grenades up at the planks in that fan room, knowing they shouldn't be able to hit that far, for me to realize what the point of the fan was.