I flew Air Jamaica roundtrip from BOS to MBJ in February.

They offer an A class fare in the market that was only slightly more expensive than the lowest coach fare (i.e. approximately $850 rt in F, versus approx $700 rt in Y). In addition, they give a 50% discount for kids, even in first, as opposed to everyone else's 25% discount. In fact, if you book the flight through DL under the DL codeshare flight number, the fares are not as good, and only the 25% discount applies.

As for the flight itself, outbound to MBJ they did give passes for entry into the DL Crown Room at BOS, and the meal on board was fine. Service was typical domestic F service. On the return you were able to wait in the Air Jamaica first class lounge in MBJ. They then boarded the entire flight, and only once all the coach passengers were on board, did they then call the club and have the first class passengers sent down to the gate. Made boarding a breeze.

For the relatively small additional cost to go in F, I would pay it again. If you are using miles, I'm not sure the difference is worth it.