I'm in the same boat, debating whether to spend the $20 to get ARMA II for DayZ (it's on sale). Except my computer runs it pretty poorly and I'm not planning to upgrade my computer any time soon.
It seems like playing with other people is the best aspect of DayZ because it adds an element of uncertainty. You have no idea if you'll get killed. You might get lucky and run into a body full of loot. You might find some friendly people. You don't have a clue but you try your hardest to survive (and maybe amass some nice weapons).
Also, playing with friends is another aspect that adds or detracts to DayZ. If your friend is clueless, hilarity ensues while they screw themselves (or you) over trying to learn and fight their way through the world. If you have good team mates as friends, you can do some pretty amazing things together and greatly benefit each other.
However, DayZ is buggy. Zombies clip everywhere, they run too fast, they hit through objects, and in true ARMA fashion, it takes one or two seconds for them to respond to a gunshot.
But it is $20 right now, which is cheaper than a new game. If you did try it, it wouldn't hurt too much.