I personally categorize the attractions at DQ into two groups: arcade games and the interactive attractions.
Regarding the arcade games, it sounds like your son would enjoy them. If you've ever taken him to a place like Chucky Cheese (kiddie pizza place with arcade games and such), then you get the idea. There is a wide selection of "classic" games like PacMan and Donkey Kong, as well as a number of more modern games.
Check this link for info on the interactive games:
http://www.wdwinfo.com/wdwinfo/dquestmain.htm
I personally didn't try any of them the couple of times that I've been to DQ, but they seemed to be quite a hit. Be wary of the height restrictions on some, and realize that your son is unlikely to be able to do any of them alone. Consider how many of these you will want to do yourself.
Sorry I can't give you a definitive answer on whether your child will enjoy or not. If you want my PERSONAL opinion of DQ based upon my own visits--I was a bit disappointed. First, the layout of the building itself is horrible. I could never tell where I was, how to get where I wanted to go, and even had trouble getting out of the place when we chose to leave. Probably 15-20% of the "classic" games were broken--either they didn't work at all or specific controls did not function. And the newer games weren't all that pleantiful.
As I said, I did not try any of the interactive games. I've heard very good things about them, so factor that into your decision.
Personally, I don't rank DQ very high on my return list. I went for a few hours with a friend while my wife and son napped back in our hotel room. I don't think I would ever set aside potential "park time" for a visit to DQ. To me, it's OK as off-hours filler, but not a must see attraction. If you have the Unlimited Park Hopper pass, then stop in for a few hours while you're at Downtown Disney. But I wouldn't recommend paying extra for stand-alone tickets.