Blades in the Dark: the actual premise of playing in a criminal gang didn't sound appealing to me at all. I'm still not the biggest fan of the setting. In play, however, it was a blast and a well-designed game.
Delta Green, expected a X-Files remash, with some COC vibes and got something much darker and more complete. Slight spoiler but the first thing you read in the Agent's Handbook appears to be a suicide note, which is a hard opening. The game then details how you as a player would have your character get to that point. It's a very dark game that is not for everyone but it really does open up a whole new avenue to explore what it would be like to be slowly losing your sanity when faced with the horrors of the unnatural.
Monster of the Week. My previous experience with PbtA games ranged from meh (Dungeon World) to horrible (Tremulus). I wasn't totally sold on trying another PbtA game and was filled with a little trepidation going into Monster of the Week. But between excellent players, an excellent GM, and a totally bonkers campaign setting, my time with Monster of the Week was some of the best/most fun gaming I've had in years.
I’ll toss a vote for Free Leagues’ ‘Alien’. I remember being at PAX the year it came out, and being kind of confused at the idea of it - shouldn’t Alien be a scenario for a broader sci-fi RPG? Why does Alien need its own bespoke system? If you had told me six months ago that my buddies and I would be over the moon about it, I would have thought you were crazy. But man, those ‘cinematic play’ one shots freaking sing.
Genesys / FFG Star Wars -- I bought these on a hunch after reading the Genesys core rules, thinking if nothing else I'd have a nice, generic, more rules light, narrative focused core than Savage Worlds. So I expected to like it; I just didn't expect to really love it as much as I did.
Ironsworn --- I came to Ironsworn with lingering skepticism based on a "meh" experience with Dungeon World. But I really liked the vibe and tone of the rulebook, and the way it explained the core game loop.
The phrase "blown away" probably gets used too frequently, but it's the best way to describe my reaction.
This was a metaphorical shot in the dark. If Ironsworn had failed me, I would have abandoned PbtA style games forever.
But instead, I couldn't believe how compelling it was to play and GM. I couldn't believe how much better I now understood what PbtA was really trying to accomplish under the surface. I couldn't believe how evocative the baseline setting was, yet how portable the baseline rules were to other settings.
And more than anything I couldn't believe it was free. How in the world could a system that had given me some of the best roleplaying I'd ever experienced be given away for nothing?