I made the journey into 21:9 (Samsung S29E790C); unfortunately it was a gift from someone who wasn't particularly tech-savvy, so it's not the greatest choice. It's a VA panel and it doesn't support freesync. I would prefer IPS + freesync.
Overall, more games that I play have felt broken than not. Lots of games "support" the resolution, but UI issues are very common. Things being visible that shouldn't be, effects only covering 1920x1080 pixels, mouse input having weird offsets, zoomed in menus so that I can't see the entire thing, etc. Combine that with the characteristic ghosting effect that I've now observed on two VA panels, an effect that I cannot stand, along with the subpar pixel density, (2560x1080 29") I'm not too thrilled with it. The only good thing I can say about it is that the speakers are really good for built-in speakers.
Even in games that do support it perfectly or near perfectly, it doesn't feel that different from regular old 16:9. I also messed around with three display surround in the past, but I didn't like that either. Maybe it's just me.
Worse is that for some reason, games won't run in pillarbox mode, so I'm forced to mess around with the Borderless Gaming software. Worse than that is that for to get the pillarbox effect that I want, I have to run the games on the left of my screen thanks to a limitation of Borderless Gaming. Every game I've found that supports borderless windowed on its own only supports it at the display's native resolution. The entire game being on the left doesn't look that nice on a curved display, although the curve is extremely slight.
The best gaming experience I've had is on a TN 144HZ Asus VG248QE 1080p display with SLI 670s. 980s and 290s with 1440p IPS weren't as good, and 21:9 has too many issues for me. My next monitor will be high, adaptive refresh 16:9.