My goodness, where would you like us to begin?! Whole books have been written and TV shows made about this. Everybody has different experiences and will tell you different things anyway. Perhaps you could be a bit more specific about what you really want to know. Or else, just jump in to any of the many other on-going discussions here on EOS. You'll find information on just about everything you need to know (and a lot more besides!) and the regular contributors are a very friendly bunch, so welcome aboard and enjoy!
Personally I would answer your question as follows: the best things would be the climate, the relaxed and healthy lifestyle, and the lower cost of living; the worst things would be, in later years in particular, coping with illness in a foreign country if you do not speak the language, and missing the support network of close family and friends. Also the stress involved in trying to get anything done in a foreign country where efficiency and speed are not part of the national curriculum.
I would recommend gathering as much info as possible about the property buying process (if that is your plan), and also look into your healthcare options thoroughly. The good thing is, you have a couple of years to plan everything to perfection before making the big move!
Very best of luck to you.