The UI is significantly worse in both CO and WoW - in fact, CO has a rather similar UI to WoW. However, WoW is TERRIBLY, HORRIBLY boring, unlike CO.
The reason seems obvious.
In CO, you start out by thwarting an alien invasion.
In WoW, you kill a bunch of things, then another bunch of things, then another bunch of things, and so forth.
Also, in CO as well as DCUO, you start with a movement power - flight, super-speed, parkour, whatnot. In WoW, about one third of the time is spent running s l o w l y back to the quest giver with nothing happening.
Both CO and WoW use the, in my opinion, rather boring mechanic of target enemy, activate power, wait for recharge, activate power....
Still, I'll probably keep on putting a bit of time in them, at least until I reach level 20 in WoW.