To be honest, yeah, Fallout 1 was humorous too, but it was a different kind of humor from Fallout 2, and most of the post-apocalypse tropes were actually played straight.
That said, I'd say that Fallout New Vegas lies somewhat in between the original two, while Fallout 3 tried to recapture Fallout 1's atmosphere but ended up hampered by some really bad world building and writing.