I've played quite a few, most over the last two years.
His Champions Trace near Lexington, KY is really a very good course. It's a stout test on an interesting property with some nice risk/reward holes and a few that simply require you to hit a good shot or two. Kentucky is admittedly a bit golf-starved, but I rate it as the third best course in the state that I've played and just a bit behind places like Valhalla.
Shepherd's Hollow near Detroit is similar. A good course and very scenic. Nothing especially exciting and maybe a clunker hole here and there, but pretty good overall.
Fox Run in Northern Kentucky has about 12 good holes and six awful ones. The last two holes are probably the worst closing holes I've seen. What really makes them amazing is the 700 yard cart ride between them. It's hard to believe that there wasn't a better hole or two lurking somewhere along that drive. The course routing is heinous. Still though, it's got to be a Top 10 Kentucky public.
Then there's Eagle Ridge in Eastern Kentucky, which is by far my least favorite course ever and the only course I've played that could potentially be labeled a "0" on a 1-10 scale. Some like it more than I do. It's probably the most polarizing course I've played, and that includes places like Tobacco Road and all the courses at Kohler.
I've played a few others too: University Club of Kentucky, Weatherwax, and probably a couple more that I'm forgetting. I think his green complexes are underrated. Some are quite good. His courses are generally quite challenging, and usually among the better or more notable courses in their geographic area. I always feel like his courses leave a little bit out there, though - that they could've been better given the property and apparent budget. There's often an awkward hiccup in the routing or one really horrendous hole. I also generally find them a bit repetitious. There are often holes that feel very similar within a single course, and it often feels like he uses "templates" between courses. There's nothing wrong with that, of course, but some of his templates aren't very good. He's usually good for at least one par 3 over a ravine to an angled green with bunkers fronting and no run-up option, for instance (he has that hole 3 times at Fox Run).
Overall, I think Art Hills does a fine job of building affordable courses with some relatively interesting greens that are usually in good condition. He's in the Arnold Palmer tier of architects for me as someone whose courses usually have one or two surprisingly good moments, but maybe a few surprisingly bad ones too.