You'll probably get the same mixed responses asking the question as reviews.
I haven't bought anything yet but have been looking off and on. The biggest things I'm looking for is one that the system works the way I like because some plain suck. Also something that the cameras aren't proprietary so that you aren't stuck buying the same make or model of camera if you want better cameras or want to expand later. That's computer based so that you can log into it from any computer in your house to see what's going on.
I don't get what they advertise as wireless cameras. Yeah they might be wifi but just about all of them still need a power plug. It's easier to run a network wire to them then it is to put a plug near it.