I had an amazing volunteer vacation experience in Costa Rica with CCS.
The program director and staff were wonderful, friendly, and had all kinds of activities organized outside the volunteering (e.g. going to a regional soccer game, to non-touristy hot springs and nature reserves, etc) to give us a real feeling for the country and the people who lived there.
My Spanish improved greatly, and I loved working both with kids/teachers at a local daycare/preschool and with residents of an old-age home (who were wonderfully patient with us as we talked with them and entertained them with our mostly-bad Spanish :-) )
It was also fun to have a mix of ages volunteering and living together.