I was just there in June on RCL's Freedom of the Seas. It was my wife's and my first time there, and first time cruising. We loved it!
We were there during the off-season for Caribbean cruises, but it was still great. We were the only ship in port, so we had no trouble at all getting a taxi. Someone above said you needed $75 including tip, but we did the round-trip taxi for less than $60 including generous tip. If I remember correctly, the taxi service charged $20 each way. Maybe during the busier winter months they charge more. Also, we made arrangements for our same taxi driver to take us back just to be safe. We later regretted that, because we were a little too conservative with our time estimate, and there were tons of taxis just sitting there at the Sunset Bar waiting for people needing to go back. We didn't want to stiff our taxi driver though, so we watched for him and took the same one back. Again, perhaps during the busier winter months getting a taxi is harder. For us, there was only about 3,600 total people there from just our ship, but during the busy months, there can be 10,000 or more at a time with several large ships in port at the same time.
As for the ship, personally, I say skip the specialty restaurants on board. Since you're on Oasis, I think you have a couple different ones than we did, but Freedom being RCL's second largest class, we still had a lot of options. We tried the Porto Fino Italian restaurant which had a $20/person cover charge. They had great food, but I personally didn't think it was enough better than the main dinning hall to justify the extra, but that's just me.
Also, my advice is to go to as many shows on board as possible, and reserve early. They're all free, but some of them, like the ice shows, etc. fill up fast. Reserve as many as you can online. They were all great on our cruise.
SA-227; B1900; Q200; Q400; CRJ-2,7,9; 717; 727-2; 737-3,4,5,7,8,9; 747-2; 757-2,3; 767-3,4; MD-90; A319, 320; DC-9; DC-1