I've started playing Dom for the first time ever this week (mostly bot games to get an understanding, couple of pvps) and I'm loving it. I've grown really tired of SR, as fun as the mode is in theory.
One, my favorite role in s2 was jungle but s3 has killed the fun there for me. It's tedious to farm, easy to fall behind, attracts too much rage from teammates. I also like that I can play one of my favorite champs, Rengar, again in Dom.
Two, the biggest reason I feel mostly done with SR, is the strict strict strict enforcement of the professional meta, even in normal games. Want to play Elise support? Rage. Want to duo top? Rage. It's ridiculous. Nearly every SR player thinks the game will break if you don't play like TSM does. It's tiring when your only choices are spamming chat and arguing over who goes mid/top/adc or having to play support/jungle every game. It really bugs me when people demand the pro meta but refuse to fill support or jungle.
Three, games there snowball so hard that too often things are pretty much over (barring a miracle throw) by around 20 minutes, but people refuse to surrender. I hate turtling out near certain losses for 45+ minutes. The game times on Dom are much more attractive.