There's DLC for underworld? The only one I was aware of was a few new costumes for Lara - not actual content ...
Anyway, I rented the game a while back, but honestly only played through the first few levels before I had to return it. The first few levels were - meh - okay. But not engaging enough for me to want to re-rent the game or buy it.
That's not necessarily a criticism of the game - I'm just kindof lukewarm to the whole Croft franchise.
Overall the game felt like a solid TR, though - minus the shoddy camera which tripped over itself quite frequently. Lara's ass is nice and all, but I don't want a 100% zoomed in view of it when I'm trying to make a death defying leap across a chasm.