Just keep playing you'll get hooked soon enough, unfortunately there's not much after you beat it. The endings aren't that great, I think it's a great game, but not GOTY material.
I'm currently on my second play through of Mass Effect, it's pretty addicting. I was play Call of Duty 4 before that, but I stopped due to my computer having some problems (Video card and usb drivers, it's pretty weird). :(