I haven't fought any of the end-game content yet (Lvl 45 BLM), so I can't speak about the coil turns and whatnot, but for the dungeons pre-50, I'd have to say I have had a lot of fun. I have no complaints really; I mean, yes, some of the mechanics in some boss fights were just downright "OMG WHY!!!??" but I was eventually able to overcome them.

It's not that hard. In end-game, the fights are labeled (Hard) and (Extreme) appropriately. I can think of PLENTY of Final Fantasy games where the fights were heavily mechanics-based. You had to have specific gear or items equipped or you weren't going to make it and they were VERY hard to beat.

People just need to suck it up and learn the fights. Find friends/people who know the mechanics and go on Learning-Runs. I get discouraged too, but you just gotta keep going; besides, it's a great feeling when you've persevered.