[Read] Combat Overhaul.
Sadly the AI will never use our skills as effectively as we do, so that wont make it much better. The main edge the mobs in GW1 had was their level up to 10 more levels than we had. Some mobs in GW2 do have skills that resemble our own too (risen wizard vapor blades and geysers, ascalonian ghost firestorms and the like) yet they dont pose any more threat or excitement than any other mob.
Castbar/tooltip would only be useful for interrupts. Thats pretty much all you need in terms of countering somethin other than dodging or sidestepping out of the way or blocking.
What i would say that GW2 is lacking is the damage specifications. Ice elementals suffer no more damage from specificly fire-based attacks than physical or even ice shards. The only thing that comes to mind that resembles anything like this is the burning immunity of destroyers and blind immunity of dredge. Even in GW1 destroyers were actually healed by the burn condition. Things like this give a deeper tactical level to the game, while getting rid of most of this makes the combat somewhat more shallow.