We've been to Deam Lake a couple times and enjoyed ourselves. We have a canoe, and did a lot of paddling around and swimming. The lake is nice, and small enough you can paddle from one end to the other in less than a month! (actually a couple hours very easy).
Fishing? Don't know.
Campsites, you want to get to the end of the peninsula as far as possible. If you are able to get to the very end, you'll be surrounded by water on almost 3 sides. The peninsula is long and narrow, but the closer to in-land you get the grassier it gets too. So there's a trade off.
The horseman's campground is across the small bay, and it's gigantic. They have horse stables, and if you take your horse, you get a stable that comes with the campsite. Pretty cool idea.
The down side is, there's not a whole lot to do there. The trails are designed for the horses, so if you walk them, you're constantly dodging horse fertilizer! But the swimming beach is really nice.
The lake is an idle zone lake only, and will have paddle boats or canoes. Occasionally someone will put in a long-john with a battery operated trolling motor.
We went for the canoeing, and the quiet. It's not a very popular park among the mainline Indiana Parks, probably because it's tailored for horse riding. So if you have a horse, a people powered boat, or just want to get away from it all, it's a really nice place to go.
If you have kids, they'll probably be board unless they enjoy hanging around horses or swimming.
