So,

A friend of mine recently purchased Descent and we spent a day playing the first campaign using the "Road to Legend" App.

This is a game we're going to be spending some serious time with and, given his birthday is rapidly approaching, i figured i'd get him one of the expansions. This begs the question:

Which?

We will almost always be playing just the two of us, cooperatively and using the App. What expansion would add the most value to us?

Shadow of Nerekhall. Good expansion, lots of new content and it unlocks a new campaign in the app. It's a bit of a no-brainer really.

Much appreciated!

I downloaded the App last night and, assuming it's accurate, the "Collection Manager" bar gets filled up more by "Labyrinth of Ruin" and "Shadow of Nerekhall" than it does any other expansion so I was going to go with one of those two barring any advice tot he contrary.

Thanks for your help.

There's more materials in the big box expansions, that's what you are seeing. Shadow of Nerekhall gets you a new campaign, it's the only expansion that's really worth buying if you want to play road to legend.