A friend and I stayed at Arenal Volcano Inn for 3 nights in late August, and we wished we could have stayed longer! The Inn grounds were beautiful, with lush greenery everywhere and great views of the volcano (but unfortunately it was covered by fog the entire time we were there!). The Inn is in a great location... It is about 10-15 minutes ($8-$10 cab ride) from the center of La Fortuna, so it is still close to all the action (bars, restaurants, banks, hot springs, etc) but also far enough away so that it is more quiet and relaxiing.
The room was safe, comfortable, and had everything we needed (and more!) including 2 beds, a TV, AC, mini-fridge,and even a hair dryer! There is also free WiFi throughout the hotel grounds which is nice.
The staff was great! The front desk ladies were very helpful ... whenever we needed a taxi to go into town, they would call for us, and they also had great suggestions for different tours, activities, and restaurants around La Fortuna.
My favorite part of our stay was the breakfast and the pool/jacuzzi! It was so nice to cool off in the pool after a long day in the heat and humidity, and the jacuzzi was so relaxing after a long day of activities and had great jets for a sore back and feet. And the breakfast was amazing... some of the best comida tipica I had my entire time in Costa Rica!... It is all you can eat, and is included wtih the price of your stay! :) There is also a regular restaurant at the hotel that we ate dinner at one of the nights, and their Arroz con Camerones was to die for! A little pricey, but convienent if you don't feel like leaving the hotel!
Overall, it was a great stay. Arenal Volcano Inn is a bit pricier than some other hotels in the area.... but between the all you can eat breakfast, AC-ed rooms, pool/jacuzzi, and friendly staff, it was totally worth it!!