Hmm, don't get a taxi from the airport - they will rip you off badly (I got charged 50 euro's for a trip to a hotel int he north - I could have hired a car for less)
The beaches on the north are black volcanic rock - expect feet and shins to be cut if you wade, the golden sand is all south where they dumped it after buying it in.
The south is where the younger tourists go (and is avoided like the plague by serious travelors as a result), the north is the reverse - all kaffee und kuchen and kitsch for the older Tourist.
But the food is cheap, the people are pleasant (at least all the ones I met) and a hire car will probably come out less than a couple of taxi fares and leave you much more mobile.
I never got to Loro Park (which is a day trip thing with an insanely early start), the desert is apparently where they shot A New Hope - think Jawa's, there are trips there too. Went to a parrot zoo in the town in the northeast, if you like birds its fine but otherwise its a bust.
Scube should be good - the water is very clear and there are a lot of shallows. Again I recommend the dolphins - if I had any organisation I'd put up the photo's on flickr or something...