I've flown TK twice-- both times BKK-IST v.v and they've been very good.. Again, nothing that really super special to make me stand up and take notice, but nothing that I'd rate as an overt failure either..
Food was good-- again, it's my opinion in economy, it's about basic food and getting fed. per se, and food really is a very personal thing.. one man's poison can be another's feast..
Cabin service was good-- properly staffed and well laid out service plan.. but with cabin service it is very dependent on the dozen or so specific crew members that are on your flight that day.
Aircraft itself was well maintained inside and in good overall repair..
Overall, I'd rate them a solid carrier.. If you get a TK flight and at a discount compared to others, then I'd say you got a pretty good deal, all things considered..