Good Things About Turkish Airlines
Great Food- Turkish has a strong emphasis on delivering great food to its business class passengers. They even have an onboard chef. However, food in economy class is only slightly above average and sometimes there is a long period of time between meals.
Flights to the Most Destinations- Turkish Airlines flies to more countries than any other airline, which is great if you want to visit smaller countries. Their route network to Africa is unmatched by any other airline. You can see the full flight network here.
Istanbul's New Airport-
Neutral Things About Turkish Airlines
Somewhat Outdated Business Class- Turkish offers mostly a 2-2-2 configuration on their A330s and 2-3-2 on their 777s. Some people do love 2-2-2 business class because it offers a better experience traveling with a companion and you don't have to deal small footwells with reverse herringbone business class seats (the new standard business class seat). I agree with these points when flying with a travel companion, but I would never want to fly in the middle section with 3 seats across.
Bad Things About Turkish Airlines
Booking on Star Alliance Partners- For this you have to visit a physical Turkish ticketing office, which are only located in a few cities in North America.
North American Departures: Atlanta, Boston, Chicago, Houston, Los Angeles, Miami, Montreal, New York (JFK and EWR), San Francisco, Toronto, and Washington D.C.
Elite Status: There are four levels: Classic (Base), Classic Plus, Elite, and Elite Plus.
Seat Maps by Plane: SeatGuru
Stopover/Free Transit Hotel- Turkish Airlines has a free stopover program that also includes a free hotel night for economy class customers at a four-star hotel if you are going to and from certain areas and your transit time is longer than 10 hours (7 for business class; Review of Transit Hotel and Program). If your connection is between 6-20 hours, you can instead do a free tour of Istanbul (review of the tour).