Arma 2 is better than OFPDR, bugs aside.
OFPDR is pretty linear game where you can't even change your weapons. IT often requires you walk about a KM to an objective where you could be one-shotted by an enemy and have to reload a checkpoint.
Arma 2 has issues with scripts not firing right in missions and crappy team AI.
It's too bad they parted ways, both games lack something the other game has. Arma 2 is using the same command menu they had in OFP1 where as OFPDR has a nice radial menu. OFPDR's vehicles suck but Arma 2's are very good.
The engine in Arma 2 is much better suited to handle the environments in both games. OFPDR's looks very rough around the edges and has 64 entity limit, so bodies disappear constantly. Arma 2's engine can handle massive battles with no bodies disappearing.
Like I said, separated both games are lackluster. Combined they could be excellent games.