Would totally agree with Varius on this Kristian - a good summary
Only items prob worth expanding on are:
Avoid San Jose - it's a dump, but that probably applies to most cities. It's much better being 15 mins or so from the city or in the "real Costa Rica".
The people are very friendly and hospitable, but like most communities there are problem elements worth avoiding. Most people know who to avoid - they can be either nationals or immigrants - you can smell trouble at 100 yards. Apart from St. Maartin in the Caribbean, we have found the people to be among the most friendly and helpful yet encountered. LE is the same - a totally different attitude to cops in the UK or US - they are more friends than anything and no "attitude".
Immigration is a.... joke. The Immigration Department is up shit creek and clueless. You can elect to apply for residency and that's no big deal, but don't hold your breath waiting for your application to be processed - that can take years assuming they can find your paperwork. But... you can apply and leave the papers with them and this avoids the net to exit the country for 72 hours every three months - or, you can elect just to take a trip to Panama or somewhere local for 72 hours (min) every 90 days.
Real estate is a boom area and has been for around six years plus. We were expecting a dip in the real estate due to ripples in the US home market, but that has not happened and now appears unlikely to happen. People from other countries have taken up the possible slack and more "immigrants" are arriving from Canada and the EU. Real estate here can be priced in colonnes or dollars and there is an obviously a substantial advantage in currency exchange when people from the EU, UK and Canada buy here.
The pollution element is mainly around San Jose - the rest of the country is fine - where around 25% is apportioned to protected areas (national parks etc).
On taxation - there is no taxation on revenue generated elsewhere - eg net earnings, tho Costa Rica is not what would normally be known as an offshore area. There are taxes applicable on businesses resident within CR and catering to the local market (tho these are relatively low). Basically you can earn whatever from net activity and no forms, filings or taxation. A further extension of that if a real offshore is needed, (often used by nationals), is to have a corp in eg Panama and direct all revenue there.