Like kirka said, it is definitely a bump up from arma 2. Better gameplay, mechanics, graphics, lags less and yeah you can also play dayz epoch with arma 3. If I were you, I would definitely buy it. Just one thing bothers me, it is not a flying simulator so if you like messing up with airplanes, helicopters and stuff just do not expect something unique. Alternitevly, you can try DCS:World for airplanes.
Arma 3 is really worth buying it.. well I haven't played it so :D I've been liking it though, watching streamers, making me jealous, and yeah Dayz is a good game too, even though I only played it without multiplayer, I downloaded it on torrent, since I can't afford those steam games.