HL2 worked well, I followed a somewhat long guide for it, let me know if you have trouble. I only played it for a few minutes before I had to go though.
re: the arcade's supported games, I haven't found a good website that has:
1. Most of the DK2 demos/games/tools/etc
2. Ratings/download counts
3. Guides to get each one to work correctly.
I imagine it's too early for that, and the steps for #3 will probably change in the next month (and be less verbose) when (hopefully) OVR fixes the direct to rift support and devs start using it.