We have stayed at Mt. Olympus several times in the past, the first time right after the water park was built and the last time two years ago.
This time when I booked we stayed at one of the Village properties (located off-site). The cost was considerably cheaper ($150 for two nights, compared to $315). We were put in building 10 (I think there are 20-some buildings in the "village"). They start at the Hotel Rome and go towards the Lake Delton Fire Department. They are all painted blue and white and have a road that runs behind the buildings that takes you to the main complex (Hotel Rome, the water park, and the theme parks) (note: at least buildings 1-10 had this road) so you do not have to drive on the main Dells drag. I was a little scared to stay at an off-site property, but was pleasantly surprised. It wasn't fancy, but a nice hotel building. Our room was bigger than we booked, with two queens and a bunk. There was also an arcade in the lobby for the kids.
We went this past weekend, April 26 - 28, 2013. On the website it stated the outdoor theme park (which is the only reason we went (our kids are 10 and 14), to ride go karts) was open Friday - Sunday, weather permitting. When we arrived on Friday it was sunny, beautiful, 65 degrees, but the outdoor park wasn't open. I even called and spoke to a receptionist days before making my reservation to make sure it was going to be open.
When the outdoor park was open, they had two go kart tracks running and one roller coaster. It was about a 30-45 minute wait (or longer) to ride the go karts. Sunday afternoon we were able to ride twice between 11:00 am and 1:00 pm.
The water park is geared towards younger children (I would say under 12). It is nice and there are a couple larger water slides, but my 14 year old hung out by my husband and I most of the time.
There is a full bar located in several areas. This was a bonus to be able to have a beer and watch the kids playing.
It is getting a little rundown (compared to when it was first opened and a smaller resort), but that is to be expected with all the families going through there year-round.
There are no restaurants on-site, except for snacky foods. Since we stayed off-site and had to drive to the attractions anyway, it wasn't a problem. But if you're planning on parking and walking the entire time, that won't be possible (unless you order in pizzas).
The theme and water parks are also open to outside patrons, so it can get really packed with people staying on other hotels and paying $30 for the day, per person, to swim and play.
Until the kids are out of school, be aware that their website hours for attractions are not accurate (and neither is calling). Don't be surprised if you show up and the park(s) are closed.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.