We just came back from 7 days in Santa Teresa. We flew from San Jose to Tambor (25 minute flight) then ride to ST (about 45 minutes). We are in our late 40's (definitely the oldest people in town!) and were with our 13 year old. Great beaches, super relaxing. Great place to learn to surf. Took tour to Curu Forest Reserve -- about 14 km on other side of Tambor, which was great. International small town -- built up over past 20 years. Touristy, but eclectic and not too American. Seems like they have a lot of lodging options for budget oriented travelers. If you don't like touristy, I'd skip La Fortuna (ultra touristy), and I've never been to Manuel Antonio -- which I hear is like being in America -- or Monteverde -- that's where all the tourists go. Things we enjoyed most if you do end up in La Fortuna were the canoe trip on the Penas Blancas River (not whitewater -- lots of wildlife) and the hanging bridges. Also -- we heard that Arenal is quiet right now -- not erupting at all. For beaches, St. Teresa is great, or check out the Osa Peninsula, Drake Bay area -- great wildlife -- VERY hot and humid though. Personally, I like the central highlands and area around Turrialba, Orosi and the Pacuare River. Have fun!
Edited: 8:51 am, March 21, 2011