I just got back from Arenal. My 5th trip, and it's the first time i've seen the volcano
However, I must say, if you are looking to do this in style, there is no better place than "The Springs spa and resort". I spent 2 days there, and it was simply amazing. This place rivals the Belagio for luxury. The bathrooms even in their worst rooms are amazing... deep jacuzzi tubs that can easily fit two people (even if one of them is a bit on the grande side). The thermal pools are simply fantastic, and they ahve a set of "lost" pools in the jungle that are very secluded. If you go during the week you may be one of, or the only people there. (we saw only one other couple when we were there).
It's expensive, but right now the rates are good.. the food is excellent, but expensive, and drinks are expensive... it's expensive all around, but I firmly believe it was worth it. This would go for $1000 a night in vegas easy.
The service is top notch, everyone speaks english, it's not tico owned (they also own "The Peace Lodge" at La Paz waterfall.) and i don't think a tico hand touched any of the construction.. it's amazingly detailed and hand crafted wood, marble imported from peru, etc.. You really have to see this place, even if it's to visit for a day. The rooms are nice though, plasma TV's, wet bar with cold beverages and a wine selection (in room). The bed is king sized with a "perfect sleep" pillow top (non-feather, so i'ts hypo-allergenic). Air conditioned. Every room has an amazing view of the volcano (assuming it's visible, but even when it's not it's still a great view of the valley).
I can't gush enough about this place...
http://www.thespringscostarica.com