Falmouth is pretty much in the middle of the island, and most of the established Jamaica shore excursions are on either end of the place, with a 30 minute taxi/shuttle ride required. Falmouth itself is pretty much an old historic city, with lots of poverty, and a nice new docking area (far from finished when I was there). I was on the first docking there, and it was quite an event. Bet its gotten pretty routine now. If you have time, do the little $10 historic tram tour of the city. Make you appreciate your lot in life.
I took the family to the Dunn River Falls excursion on a previous cruise, and we did enjoy that. Last trip we shuttled to a private beach in Montego bay and just lounged on the sand for a few hours.
I hope more local excursions get established, and some cruise ship money finds its way into the local Falmouth economy to add local amenities. I will be going back with the whole crew between Christmas/New Years this year, so I will await your take on how the place might have changed....
Final note... stay with a group. Not always the safest of places. Had to run some local 'entrepeneurs' away from my teenage boys a time or 2, even at the tourist frequented places.