What is a good RPG to play for about 10 sessions?
Assuming we’re playing every week, 10 sessions works out to 2-1/2 months, which I would consider a short campaign. For short campaigns I tend to steer away from D&D or Pathfinder, and I look at some of my underplayed RPGs. Shadowrun or In Nomine are good choices for me, because I find it easy to develop shorter story lines for these games. I also find that, since my groups are very much in to fantasy role-playing, these make for nice change-of-pace games; my players will enjoy them for the short campaign, but be ready to come back to their D&D campaign once it’s over.
And that’s really the main use for a shorter campaign for me, as a palette cleanser between chapters in my long-term campaigns. So that being said, the one that will work for you will largely depend on what you play regularly. If you’re in a long running modern or sci-fi game, a short dip into fantasy might be your best bet, for instance.