The biggest thing you missed on your first playthrough?

I'm just wrapping up Act I in my second playthrough. I already know I missed breaking the Shadow Curse in Act II my first time, no idea how that happened. I didn't realize I also missed the githyanki creche / mountain pass. Thought it was just two different ways to the shadow lands so I chose the grymforge elevator. I also did things in a very ADHD order the first time and I'm finding out lots of new info just by changing my order of operations. Love this game so much.