A further advantage of limiting how many powers the user can have active (and further such neverwinter tier them) is that it makes the ones you do have more special.
It also gives an argument for the lowest tiet (spam tier) being continous. If it isn't you are just going to cast it again anyway.
Been playing a "rogue" in swtor and as they give me more abilities i'm starting to realize that while i do enjoy rotations
1. It is not clear enough for me. I want it as 1-2-3-4. If i remember correctly age of conan dis this well.
2. I do not enjoy deep rotations. I want.me right hand on the mouse and me left hand stationary on left side of keyboard.
Also i do not enjoy having everything on cooldown. Especially global cooldown.
Neverwinter does this well. It lets you have 2 attacks that you can do constantly and those continue as long as the button is pressed rather than happening and then waiting for cooldown.
Then it gives you up to 4 special attacks that are on individual cooldowns along with two extra specials who share a chargeup.
Of course there are many to chose from but they have to be slotted into those slotts.
Edit: and the reason i like the neverwinter approach more is because it lets me feel i am doing something the whole time while letting me watch the world rather than having to watch the attacks the whole time.
