For a comic with a title like CAD, it's surprisingly not about video games very much. Buckley's game references are usually dated, and you get the impression that he doesn't play many video games. So, you are left to look at his writing. Unfortunately, none of his characters act like human beings. He handles dramatic writing incredibly poorly, and no one really grows as a character. That is fine when you are doing comedy, but it falls apart when telling an overarching story.
The art is amateurish at best, but that can be ignored if the writing is good. Again, it's the combination of poor writing, poor art, and the fact that Ethan is a Mary-Sue (a character archetype that I cannot stand) I can't say I hate CAD, just like I can't say I hate a pile of dog droppings. It is just there.
Tim Buckley opens himself up to internet hate very easily. As a person, he doesn't seem to interact with others well, yet he puts himself in a public venue demanding attention. In addition, he surrounds himself with sycophants on his forum, and bans anyone who speaks ill of himself or CAD. Nothing attracts negative attention than ignoring your critics or people who honestly try and help you. It just encourages those critics to be louder, and strengthens their arguments. Still, he has secured internet infamy, that's a sort of fame in and of itself.
It's also impossible for me to type up any issues that haven't already been well established on the internet. I'm just one of many CAD detractors. Besides, the haters produce things that are much funnier than CAD could ever hope to be.
I'm not surprised so many people on this forum like it though.