First off, a warning: The staff at this hotel do not speak English! I think they had maybe 150 words of English between them, and I knew about 20 words of Spanish if I'm generous. If you do not speak Spanish, this is probably not a good hotel for you.
That said, the staff was extremely friendly and helpful to the best of their ability, including taking the time to write things down in English (probably with some translation software help) to confirm things with me.
The offered horseback riding was fun. If they mention a "boat tour", it's actually a kayak rental. Just you, no guide. I discovered that when they took me down to the lake, gave me a paddle, and said "see you in 2 hours." It turned out fine and I enjoyed the solitude, but it wasn't what I was expecting.
There's a nice nature walk through the forest behind the hotel, too. The food in the restaurant was quite good for the price. About twelve buc for a fairly good steak, rice, and vegetables. Service wasn't especially fast, but the food and price were good.
There is no hot springs at this hotel! If that's your reason for coming to Arenal, go elsewhere. The staff recommended the nearby Los Laurelas springs, which is more of a water park than springs, it felt like. (Good water, lots of temperatures, but I've no idea if it was spring-fed.) It was 10 bucks, but a 25 buck cab ride each way which made it more expensive.
Overall, it was an unexpected adventure but a good one in the end.