Very disaapointing, with an engine that shows its age so badly it's embarassing.
I was able to play ArmA, the Czech version, at a friend for 6 hours, and I was shocked how few things have actually changed since OFP. With a better-than-average system (2.6Ghz, 2GB, X850XT), framerates were below 25FPS 80% of the time. It was possible to increase them by turning off details, but then the game would look REALLY dated, probably 2002-style. It would really look like OFP with a few more textures then. I'm talking about 1024x768 here. Embarassing.
Unit movements have not improved, with everything that moves you can see the underlying programming shine through, like infantry turning in 45 degree angles and more of that sort. This is quite an immersion-killer for me when I spproach a game with today's expectations of realism.
I really liked OFP, but maybe now I am spoiled by how good - and realistic! - games look today. ArmA just does not live up to ANY of today's standards in my view. Btw: that's true for sound as well. No immersion here at all, *sigh*.
Why did I not write anything about the gameplay? Because nothing has happened since OFP. You can take a AI soldiers position when you are killed, but that basically seems to be it. Could not test multiplayer, so I might miss a few things, but in the SP I tested, I felt right at home - in Operaton Flashpoint :-(..
So, realism is still there, a huge island as a playing field is there, some nice dynamic time of day and weather are still there, well, all that OFP had already.
I'm giving this 5-6 out of 10 for the potential it might have when maybe everyone has a Nvidia 8800 in their system in a year or so. It might be playable with high quality visuals then, and maybe (I doubt it a little though because maybe others will be disappointed too) there will be an active, grown-up community around it then.
But until then, I will not spend any money on it.