Wont be able to play until tonight and I had two non-spoiler questions.

1. How linear is Dead Money, is it linear at all?

2. Is there any "collect this" type stuff in Dead Money, like the briefcases in OA, or the ingots in The Pitt?

Like I said in an earlier thread about Vaults.
It's better to have a smaller vault with the right amount of content than trying to stretch one out into a messy maze.
Dead Money is in the latter category.
Lots of nooks and crannies to explore but overall there is little to no reason.
Maybe for a single unique or two but hardly worth it most of the times.

1) farily be carful at the ending if you want to keep on playing after it

2)no real quest in need of collecting quest some minor tasks for exp for collect x amount of some stuff or kill some things