I had a pretty decent experience flying Turkish about 2 years ago. They didn't have flights to Nepal, so Delhi was the closest I could get (with them). I did have a little bit of difficulty communicating with the airport staff as most of the ones I encountered were not able to understand and respond in English, and I needed to get a boarding pass replacement as I had misplaced mine. I managed to make my way through them to the right person, but they all seemed helpful and concerned (to at least understand the issue)!

The flight to India felt like flying on an Indian aircraft. The in-flight entertainment options, food menu, people, the smell; and the overall atmosphere was very different (more 'Indianish'). Nothing wrong with that, just felt and seemed such!

Since Istanbul is in Europe, make sure you do some research around the duty-free liquid purchase policy (if they still have it enforced). I had a terrible time in Brussels on a different trip. I've been trying to stay away from Europe stops since then..      

There's nothing else remarkable or worth mentioning from what I remember. So, take it easy - and enjoy the travel! 

BTW, Istanbul looked stunning from the sky.. :-) 

~@~