It is fantastic, seriously. You play single player campaign its good, you keep playing missions being made by the community (Check out Druid_, he makes amazing missions http://forums.eagle.ru/member.php?u=60317). Then you get to multi-player. When you fly mission with another person, anything can happen, so many variables, a unique experience every time you fly. This is the same for Black Shark and Lock on, however my personal favorite is the 'Hog.
As for things to keep you going, just a personal drive for perfection, to learn about the aircraft, to know its limits, to know what it can. The great thing about DCS and Lock-On is, once you get to know something, it is entirely satisfying. I would definitely say it is something special.