We played Star Fluxx, Star Munchkin, Dixit, and, of course, Bomb Alley.
22.214.171.124.5 Slope & Crest Hexsides
Both Slope and Crest hexsides have a Height of +1. However, only Crest hexsides may individually block line-of-sight. Slope hexside are part of a Hill formation and any line-of-sight checks are made from the Hill hexsides.
So I think Slope depictions don't block LOS.