Pros: excellent grounds, many trails to explore, lots to do on property, food and drinks at the restaurant were a huge plus, breakfast buffet was our best breakfast on the trip, wildlife surrounds you, free morning tour was a nice introduction to the grounds, hot tub and pool were very relaxing, no shortage of adventure to be had here, great customer service at front (especially Carla).
Cons: Rain - not their fault but rainy season is as described - driving, consistent rain - it will be raining probably about 75% of the time (this was July 2014). Quite a ways from La Fortuna and road can to Arenal Lodge can be rough.
Bring very good rain jacket and extra shoes and also many changes of clothes. Also bring a flashlight for night walking.