What all is missable in the game?

I've heard a few people claim if you don't do quests in a certain order (aka finish an act before side missions are done) you will miss out on rewards and skill points. There's also the whole bandit quest where you get to choose between the rewards. Is there any more quests like this? is anything missable?

Thanks.

Not a whole lot. The thing most people will probably miss is that you can open the passageway in act 2 that was blocked before - this will grant you a passive skill point. It is rather obvious from the storyline, if you actually read it :). Other things include special named mobs, e.g. the crab in the Flooded Depths or the Great White Beasts - those are named mobs that will give a special reward in town, but you won't miss them if you explore all areas of the game.

Seems like I already lost a passive point then? I explored every area and did every quest but I don't see anything about opening the passageway quest.

It's a real shame there are missables in a game like this.

I'm pretty sure that you can go back and do any quest you may have skipped. I know that I have personally gone back to do normal diff fetid pools after I entered cruel difficulty. Also the bandit quest is unmissable, you can't progress to act 3 without having completed it in one way or another.