Or should warring with the Thalmor have been part of the regular game

Neither. I think it would fit best being dealt with in its own game.

Dude I heard about this DLC coming...it's called.....Dawn......something.......Dawnguard!
I do hope it comes to the PS3.

any excuse to murder more of those stuck up thalmore is cool with me.

This. I don't get why people are so obsessed with the Thalmor? They just won't fit into a DLC for Skyrim. Why not leave it to TES VI:

Fallout 3 handled the Enclave pretty well with Broken Steel.

It would be nice as a Side Quest in the next DLC, just maybe introduce them for a while.

This.

Repelling the Thalmor from Skyrim, outright Talos "reinstatement", yes. All out war? No. More like the last DLC as a prequel to the next TES.

I think a whole game (that might seem like a little much to some) would be better fitting. To have whole quests that take days , that have you siege a town, city, or castle would be epic. To lead men and women on the battlefield, to have a changing environment that looks war torn and desolate. To bring the war (I'm longshooting it here) to the thalmor, to crush the elves, or join them and establish a new governed nation ruled by elves for elves and people who like man slaves.

I'd rather a DLC that greatly expanded the Guilds.

I could see it being potential DLC, but i think it would be better for future games.

I think a DLC where the Thalmor begin an attack on Skyrim could be quite good. That way we ge to experience the beginning of the war but the majority of the war, which can't be done in a single game, is left for the next game or something. It could go something like the Thalmor attacked Skyrim, resulting in Skyrim defending itself and the layer must help to weaken and push back the Thalmor. After the DLC is over the rest of the Empire would unite to stop the Thalmor and defend Skyrim from what could be seen as an unprovoked attack. The rest of the war could be either the next game or an in game book in the next game, similar to how the last war was in Skyrim.

Double this.

This has been discussed over and over again and my opinion is still the same. A war with the Thalmor and the Aldmeri Dominion is too great of a gaming opportunity to be left in a DLC. It deserves a game for itself.

Could very well be both, kind of. The current engine is clean enough to dev a whole new game on. To merge into Skyrim, no probably not, too much to meld, too many variables and quests will get majorly glitched, guaranteed, if they're parallel. BUT, engine in place, you can't rule out a "Skyrim 2"/TES VI:Dominion.