I partly only come onto threads discussing 21:9 on here to see what kind of fanatical and dogmatic crap Tegiri Nenashi has come up with now. Check out his old posts - he's on a veritable crusade against anyone purchasing 21:9 monitors. Tegiri - you're boring at this point. Crawl back into your hole.
Personally, I am 100% buying a 29" ultrawide in the next few weeks, and I've been planning it for months reading everything possible about the format and various screen options, and the overwhelming response from people *WHO ACTUALLY OWN THEM* has been that they are fantastic, and something these people will never go back from. It seems from their reports that the extra width gives enough of the "surround/eyefinity vibe" without the extra GPU horsepower required or the fishbowl effect on the edges, is easier to adjust for when games require fixes to make it work (something that is becoming increasingly rare), and for gaming or productivity work specifically, is absolutely fantastic. For media consumption, it's a hit or miss bag, with movies being fantastic, new 16:9 TV shows suffering black bars and older 4:3 shows crappy with the amount of screen lost.
In my reading, it does seem that many people are saying that Freesync or Gsync are absolute game-changers for monitor developments, and many people harp on about the benefits of higher refresh rates though it does seem that except for ultra-competitive egamer uses, there are diminishing returns for ultra high refresh rates. For example, the jump from 30 - 45 fps is massive, 45 - 60 is huge, 60 - 75 is big, 75 - 90 is very noticeable but also starting to be diminishing, 90 - 120 becoming less important for smoothness, and 120 - 144hz mostly about the "feel" of response times than anything else. Of course this is a little bit subjective, but the point being that if you're hitting 75 - 90 fps, it seems to be a valuable and worthwhile jump and also an acceptable compromise for other features. I say this, because 21:9 screens with ultra high refresh rates are few and far between, but those with 75hz are readily available and a few with up to 100hz either just or soon to be available.
All in all, I'm getting a 29" ultrawide IPS with 2560x1080p at 75hz (freesync enabled) in the coming weeks, and I cannot wait for it to arrive just in time for Fallout 4. I just can't afford the bigger 34" ones with 1440p UW resolution, despite really wanting one. And even though I have an nVidia GPU, the Freesync monitors will work with 75hz and adaptive vsync (via DP connection) which will suffice for me for now. As the tech progresses I may upgrade in future, but I'm not a competitive gamer and this model (LG 29UM67) seems to cover all my bases and should allow my gtx970 to get solid frame rates until I can afford a brand new build.
Anyway, here's a youtube channel with some fantastic coverage and examples of 21:9 gaming and some objective analysis of the benefits, drawbacks, and little idiocyncrasies which exist in various games.