I played DA:I having played Origins and skipping DA2. The lore is all there from Origin, but of course I didn't recognize any of the characters from DA2. I think having played Origins will make familiar with the lore and the world, but knowing individual character's backstories won't have much impact. Like anort3, I'd recommend at least playing Origins. I think it's available dirt cheap on EA Origin.
VTMB is one of the best roleplaying games of its era. You'll love it, especially if you dig vampire or horror games, or just RPGs in general. Watch out for bugs, though; I'd recommend getting the unofficial, fan-made patch as well as the widescreen patch.