I bought it and I love everything about it.
There seem to be a lot less glaring bugs than in the original ArmA, and the graphics are amazing when the only real "high-end" part in my computer is a 4890. Running on a dual core, it can handle most battles with many things happening at once.
Online is about the same as ArmA 1 with a new world to play. Most of the servers are evolution or domination. Few servers run the unlocked version of either modes, and even fewer run any sort of PVP. If you want to play PVP (and trust me, you will after playing against AI with expert marksmanship), jump on any of the two AToW servers (just filter for atow), ones in the US, and ones in the UK. PVP is quite fun, and gives you a more rewarding feeling than dropping a few AI. IC Arma, and AToW (Arma Theater of War) will be starting their ArmAII campaigns within a month or 2 once they have all the appropriate plugins done and ready.
The Campaign itself is a bit... odd. The voice acting makes me want to tear my ears out, and the AI makes me facedesk, but it's a good time killer if you're bored. The mission editor really shines, and is quite a bit better than the old one in ArmA, making SP missions is a sinch, just plop a few units, place a few triggers, throw a tank in the mix, and it's a party.
In conclusion, ArmA is an absolutely fantastic game, with good gameplay, graphics, and very negligible bugs.
P.S. This isn't an advertisement for a different clan, but joining a tournement such as AToW is a magnificent experience, and gives you a much more involved feeling with its heavy teamplay based warfare. They run a teamspeak server, plus a server for pubs and a server for the tourney itself. Try it out
here! (battle days are every sunday @ 17:00GMT). Also, feel free to PM me with any questions about the game.