This is a nice question. I love surprises! Mostly love them.
Bad surprise: prepping for Coriolis, super excited to try out the next iteration of the Mutant engine (which I’ve played and loved in Mutant: Year Zero, Mutant: Genlab Alpha and Tales from the Loop). Doesn’t work. All the good stuff is gone, lots of dumb new things got added that don’t really work.
I pride myself on being really good at pulling out the core essence of any game through reading and play. When I can’t find the fun, I tend to blame the game. Sometimes I know it’s me, though. It’s not me when it comes to Coriolis. Or Rogue Trader. Or 13th Age, although in that game’s case it was 100% a stylistic mismatch. But it was a surprise because I really thought everyone would be into the advancement grind. They were not.
Good surprise: Montsegur 1244 the first time. It was an early foray, for me, into the totally systemless, GMless, freeform space. It’s got some soft emotional manipulation build into it, mostly via the march of scenes toward an inevitably tragic end. I also chose a way-too-raw characterization for my main and secondary characters. I was left really shaken, and I gotta say it continues to surprise me. I’ve got surly old grey gamer bona fides which usually comes with a big dose of cynicism, and my experience with Montsegur was undeniably powerful.
Another good surprise: King Arthur Pendragon. If “trad” games had built their traditions upon KAP, I don’t know that I’d have ever moved on to other schools of design. This continues to be, for me, the most effective game for building a big, sprawling family drama with super deep investment and unironic play. Just amazing. I’d love to get it going again someday. I’ve fiddled with other throwback “oh hey remember this?” games but this is the one time I felt like I’d uncovered forgotten gold.
And my latest good surprise: Bluebeard’s Bride. Super interesting design, weird structure, doesn’t feel like anything else I’ve ever played. Ostensibly PbtA but really far afield in that style. I had the advantage of having played it with the amazing Katherine Fackrell at the helm this year. But it surprised me anyway on so many levels. Mostly I was intrigued by how experimental it is, like, as in it not really working or playing like any other RPG while still having the trappings of conventional play.