I'm on Death Valley (about mission 5). Really enjoying it so far. For a new Arma player like me, I found it much easier to get into than the Showcases. Enemies are introduced gradually, ramping up in number, so I have got better at working out who is shooting at me. Excellent introduction to Arma. New players are going to have to do a lot of fiddling with controls to work out what to do, but that's far preferable to a long hand-holding tutorial thingummy in my opinion.
The odd crash in seemingly random places (e.g. after an autosave near Blackfoot, or after I crashed my UAV), but nothing serious or reproducable. Struggled a bit with the briefings at Maxwell as well - not always clear where to go in order to check in for a briefing and get the next mission started. Once I had to reset, because nothing seemed to be happening.
Great stuff BIS.