I agree that the instances did detract from the action of the map, and the removal of an entire team's heroes led to a very one-sided battle on the gaming field, however I think they can be reworked rather then removed. The current "event" system you have also detracts as it directly interferes with gameplay. Here's what I suggest;
Reinstate the instances, but add a sort of hearthstone item to each player, what way when they enter an instance, they can all hearth back to their town in the event that they need to help defend. Maybe an ability called "instance que" or "dungeon finder" could be made so players can enter an instance without having to run to it. The horde and alliance icons for the heroes could be removed in place of such an "enter instance" ability and the like so time is not wasted away from the battle physically moving to it.
Upon defeating instance bosses, do not just drop loot, but rather award players with an item (trigger them to appear in their inventories for those who are within a certain distance during the kill). This way all players that participated get the reward, and rewards the whole team enough so that they gain advantage over their enemies who did NOT raid. This also removes the frustration of going through all the trouble to raid and not getting anything out of it (like real WoW raiding).
The Deathwing unit should be scaled up a little bit. Its such a nice model and its too small to see the fine features.
I also think you should use Kwaliti's Lich King model. Its too darn cool to pass up.
http://www.hiveworkshop.com/forums/models-530/lich-king-154837/
IN short: it would be a shame to have that nice terrain you made for the instances go to waste. Having them does spice of map variety a bit, but needs to be done in a way where it does not benefit he opposing team by removing their enemies from the battlefield for extended periods of time.
Well, these are just my ideas. Take them for what they're worth. Excellent map so far. Excellepnt terrain, constant effort to balance the heroes, accurate WoW theme...keep up the outstanding work.
-VGsatomi
Approved
I'm going to make the alliance Shaman class a dwarf as apparently thats a new class combo for Cataclysm 
