I am currently playing and enjoying Operation Flashpoint Dragon Rising bought in a Steam sale a couple of weeks ago. That the game is being heavily discounted so soon after its October 2009 release indicates that it was far from a commercial success, a suspicion re-enforced by Codemasters announcement of a cessation of support for the game on the 16th February this year.
My guess is that the game failed commercially because it fell between two schools. It is much slower paced and somewhat harder than traditional run and gun shooters. I imagine that many Call of Duty fans will be put off by a game where you can go 20 minutes before seeing an enemy and then die instantly from one bullet. On the other hand fans of earlier Flashpoint games may feel the game lacks realism and is too easy: You have a magic radar which pinpoints enemies with a red dot. Enemy AI is not all that smart and your team medic can cure every injury short of death with a single injection of morphine.
I never really got into the earlier Flashpoint games so I am enjoying the single player component of Dragon RIsing for what it is: A tense squad based shooter that is slower paced and more challenging than a typical shooter and requires careful tactics to overcome mission objectives.
My only real gripe is with the checkpoint save system. A typical mission has several save checkpoints that are highlighted on the map marking out a path to the mission objective. Most of the time I prefer not to follow the checkpoints - instead plotting my own route using the terrain for best advantage. The game is open enough to allow this but it means I don't get the benefit of the checkpoint saves. Knowing that you can lose an hours progress due to a random bullet is a bit of a downer. It does increase the tension of the game however and I find that one mission per night is pretty much my limit before I need to take a break.
The dropping of Codemasters support does not bode well for competitive multiplayer but I believe the game has a co-op mode which could be fun.