They appeared to draw a large crowd along with a number of people who would stop and listen to various songs as they went through the fair. Since I wasn't inside the event I could only gauge crowd reaction by the applause. To me, it didn't sound overly enthusiastic, nor did it seem too tepid. I thought the medley was well received, along with various songs from their heyday.
I heard a range of comments from those outside the venue. Anywhere from how great the music was, to how bad Dennis' voice had gotten (several people explained that Dennis was no longer with the band), to how Dennis got screwed or how Dennis was a whiner. My overall impression of the people I saw was that they were reasonably pleased. I think Styx is truly a nostalgia act and for the folks going, it was a nice night to relive a little of their youth. Not a bad thing at all.
Having watched parts of their stage performance and listening to them perform, I know they are not a band I would enjoy seeing. I say that with no malice towards anyone here. I didn't like some of the changes to their material (just as I believe some of you don't like changes Dennis has made to the material he uses). It's just a personal preference. I am sure that Kansas (or at least I assume he will) will post a review and I'd bet he enjoyed the show. Which is great.
They are solid musicians and it was a great night to not see a show in my case, so I guess they were fair at the fair.

Peace