Of course one could argue that the plane was just taking a shortcut over the small part of Turkey territory. The problem with this is that Turkey has warned Russians on many occasions to not do that. But in my opinion it does not look like there was any threat to Turkey.
In principle the Russians have become very cocky near all NATO borders, and Turks are the least PC NATO member, so one can say that Russians had it coming and it looks like they finally found their equally crazy nemesis. Anyway, the situation is alarming and it is not yet clear how the following actions would unroll.
The first reaction from Putin does not make it look like Russia would admit their fault, but I think that he is rather reserved.
My condolences go to the parents and relatives of the killed pilot.
Edit: Changed two paragraphs, added one more paragraph.
Edit2: It looks like Russians flew over Turkey territory towards their target zone (see the map provided in this thread) and then began to fly in circles over Turkey territory. They were shot at the second entry.
I do not know why Russians choose this route as it does not seem to be the most optimal one.
The length over Turkey territory is about 1500-1600 meters, SU-24 flies up to 360 m/s so it was about minimum 5 seconds flight, but as it was a second entry, I guess it does not matter that much.
Anyway, I think that both sides acted in a very unwise manner.