I'd also add you should look at Comfort Class to see how that prices out. It's TKs version of premium economy. 45" of legroom, leg/footrests, lots of recline, upgraded meals. Some say it's like an older style Biz seat. I flew a RT BOM-YYZ in Dec. in the same 777 you get from IAH. Comfort was only about $100 more expensive than UA (or anyone else) in Y class on that trip - and on some days, comfort was even cheaper than regular economy on TK. Was well worth it.

IST is a big airport, and the signage is not great. Connections are a lot better than they used to be. You come through a central security checkpoint (security used to be done at each gate) but there is one for domestic connections and one for international - these are not well signed as to which is which - make sure you go to the right one, so you don't wait in the wrong line. Be prepared for a lot of walking though. Otherwise, it is fairly smooth. If you have access to the lounge, this is one of the best *A ones, IME.

Also in terms of connections, many on here say when irrops are involved, it can be bad. However, on my return, we left YYZ four hours late (loading the aircraft with bags took a long time - it was one of those days that was -40 in Jan) which was going to make me have to literally run to try and make my connection. However, TK staff were at the end of the jetway upon landing in IST for the several of us connecting to this flight (as well as another flight with a now close connection) and escorted us through security and to the gate. Was very impressed with this - as I was pretty sure I wasn't going to make it (though to be honest, wouldn't have been too disappointed to be 'forced' to spend a day in Istanbul).