It is a really great game. When I think of my most favorite ideal setting ever, Fallout 3 delivers. So many great stories/tales can be made from Fallout games or any piece of Bethesda lore for that matter. I have to admit, without the DLCs, I would've been pretty disappointed as the game halts the gameplay. The Fallout 3 DLCs is probably one of the main factors that makes this wasteland so great. I mean, think about it. Without the Fallout 3 DLCs, we would be missing out on several diverse features(Which would also pave the way for influences in future games, like New Vegas). Like the following:
Increased level cap and continuation of life to remain
Gauss Rifle + Chinese Stealth Armor(A great combination)
Anchorage war simulation for players who have a predilection towards warfare(Not that I'm one of those players)
The Pitt's hardship story + atmosphere
The Brotherhood Of Steel's additional storied legacy of the East. Either ending up as prosperous or adverse for them in the end.
Point Lookout's perfected world and an unimaginable amount of potential lore-stories.
Mothership Zeta's powerful guns and great science fictionated lore.
Apart from Fallout 3's "differing" from past games as many like to bring up, Fallout 3 is a great game overall and I also, love the DLCs as you do.
Enjoy it, partner.