1. They are currently [censored] when it comes to equipping items. For example I currently have an Archmage robe on Arenea (a mage) and she never equips it. She'll equip heavy platemail, but not the friggen robe. Now she has equipped the Adept Hood, but is otherwise naked, still the robe is lying in her inventory and she won't use it! Ridiculous. And she seems to randomly equip the hood, sometimes she has it and sometimes she doesnt.
She also has an uber glass bow in her inventory, but decides to instead use her default hunting bow that does very little damage.
Why not just let the player choose what items they have equipped?? It would solve a lot of problems.
2. Companions keep blocking you in narrow areas (such as doorways) which is annoying. It's not game breaking because I've yet to become completely stuck that way, but it's annoying to have to spend 10-20 seconds navigating through a doorway because of your companion. Why not just let players bump them out of the way automatically if you walk into them?
3. Let us see their stats! It's frustrating when you have no idea what skills a companion has, so you aren't sure what type of weapon etc to give them. If you don't want to show all of their stats, at least show what main skills they have (like light armor - one hand) or something to give us a hint.