The scale of this game really staggers the imagination. I won't deny the common complaint that a lot of the places look the same as each other, but that doesn't change the fact that there are a heck of a lot of places and even if they reuse a lot of geometry that doesn't keep them from being designed with simply astonishing attention to detail. Before digging into the new quests, I meandered around to check out some of the locations I never got around to visiting the last time I played the game, and they're packed with stories and atmosphere of their own (the letter to the editor from an angry nerd in the Hubris Comics mainframe, for example, or the crazy radioactive maze underneath the Falls Church metro station with the unique flamethrower as a prize at the end of it.) Even if there were no new quests, an extra 10 character levels to encourage complete exploration would have been worth the money. Uh, nobody tell Bethesda that.
As far as the specific DLC questage goes, so far I've only completed Operation: Anchorage. I do have to admit that it drags a bit at times, as the whole premise is that you are completing a military sim and you can't leave until you've done the whole thing, which takes hours and isn't really any more than some straightforward combat. And while I enjoy fighting in Fallout 3, it's really not Call of Duty and shouldn't try to be. There also isn't much depth to the story -- the conceit is that the Brotherhood Outcasts are trying to get into an armory, and apparently the simulation needs to be completed to do so, and you're the best choice to make that happen. There's nothing actually unusual about the sim itself other than some pretty arctic environments, no Matrix-style breaking of consensus reality or anything (unless you count smarting off to the NPCs about how they're not real.) You finish it, you go to open the armory, and that's that, quest complete.
Though that being said -- once I opened the door to the room full of goodies, some of the Brotherhood members started arguing that I shouldn't be allowed to just take the loot, and the argument ended in a wild internecine firefight. When the chaos subsided every single person on both sides was dead except me which wasn't intentional I swear. When I realized nobody was going to run in to ask what the hell that noise was because they were all already here in varying numbers of pieces, I did the only honest, moral thing I could... I gently, respectfully ransacked the whole complex and removed everything in it and from the bodies that was even remotely valuable. I now have enough sets of Brotherhood Power Armor in my bedroom closet back in Megaton to outfit a regiment.
I think Protector Sibley would have wanted it that way.
If you're in the mood for more wittering on the subject of Fallout 3, incidentally, you could do worse than to check out this compilation of articles written in gaming blogs about it last year.