I hated the metro system, personally. All copypasta, never anything worth shooting down there, yet plenty of things you had to shoot.
I kind of half to agree, the metro system really seemed like one of the less rewarding places in Fallout 3 to explore, and yet you had to explore them to reach most locations in DC, which is really what bothered me. I wouldn't have hated them as much if I didn't have to go through them to navigate the city, so I'll be glad if I can move about New Vegas while remaining above ground.
But it seems to me like it's pretty much an unofficial law that RPGs must have something like dungeons in them, I certainly can't think of one that did not which I've played, so yes, I'd say they'll be in the game. The question is how many there will be, what sort of places they will be, what's in them, and such, THAT, we can't say yet.