Hi Selini,
It's awfully hard to give such generalized advice on where to go in a country. Some questions come to mind.
1. Do you want to stay put or move around within the country?
2. When you went to Mexico, Bali and Greece, how did you travel. A travel agent always asks about past holidays, the good, the bad and the ugly, so the future trip can be planned based on past experience.
3. When you are visiting a new country and are uncertain of what there is to see, I recommend you drop by your local library and check out a guide book on Costa Rica. You can visit your local book shop as well. I consider one of the best guides is Moon Handbooks.
Also visit the Costa Rica Tourism Board site at
http://www.visitcostarica.com/. Regrettably this is a high-tech site, hence it's rather annoying to get around. I wish they would KISS!
These two are private sites, like a travel directory:
http://www.travel-info-costarica.com/ and
http://www.govisitcostarica.com/Once you have gone though a guide book or the web site, you will pretty much know what you want to see, where you want to stay and what you want to do. That's the time to come back on line and get specific advice.
.