Well I went to Devry and took a few online classes. My degree is Computer Information Systems with a track in Computer Forensics, which probably covers a lot of the things you would cover in Criminal Justice.
If you are taking a "blowoff" class, or if reading the text book will be enough for you to learn from the class, I'd say go for it. You cant replace the face-to-face interaction, and someone explaining things to you, giving examples and if you have a question you just raise your hand and get an answer immediately. So in ex: taking a programming class online is a terrible idea, because there are too many variables and different situations that can come up, and you just get a better understanding of things face to face.
But with the Forensics classes I took, I had no problem taking them online because its pretty straight forward, heres what you need to do, this is how you do it, here is what the law says, take a quiz and your done. Nothing that you cant learn by simply reading a textbook. There is still online discussion which does make things a little more interesting, or a pain in the ass if discussions are graded and you don't really have anything to add.
At least that was my experience with it.