For the 8 seconds that you have the spider web ability, you lay web behind you in a straight line, like the spiders do. Any time you turn sharp(ish)ly, it starts a new strand. When an enemy tries to cross a strand, they either move really slowly or get stuck, I'm not sure (either way, the boss didn't manage to escape my web during the time it was there, which I think is about 30 seconds). It's actually a really cool ability and it's been implemented really well, especially for an ability that you only get for 8 seconds at a time from a single(?) item. When I get around to making mods, I think I'm going to have to make a spider form, so get to play with it more.
Charge shot still homes in on enemies without enemy targeting on, you just can't dictate which enemies. I think it always goes for the closest ones, but I'm not sure - it sometimes seems to avoid passive creatures a bit, but I may be mistaken.