It's got an interesting history. It was actually created as a reservoir for the Miami & Erie Canal. You're right as far as being shallow, the last chart I saw shows a max depth of 8' (at two small spots towards the middle of the lake), but it's definitely got surface area. My FIL dinged up his prop the last time we were there when he got a little too close to one of the islands. But I think he said it was his own fault for not paying attention to the markers. We are still new to boating on our own and we didn't have any problems up there this summer.
I know algae was a big problem in the past due to the huge amount of farmland runoff, but they've been working on it and it seems to be getting a bit better. I really wish they would work on dredging to get more depth. I think that would help a lot with a lot, not just the algae.
Can't help you with seasonal rates because we just go up with family occasionally and stay at Kozy. There are a lot of fun little hole in the wall places around the lake.