We stayed at Sandals Montego Bay Jan 08. We also heard all the talk about poor diving and scary places.
As a fairly new diver (then), I totally enjoyed my diving!! Diving in Texas, Houston Area, is mostly man made lakes. You want vis? You go elsewhere!!
Other than not being able to party all night to get up at 7 and drag our gear down to the dock, we saw some pretty cool things. My personal favorite was a huge ray that we just followed around for a few minutes. There are a few small swim throughs and if you like to just watch marine life, take it slow and easy.
We also did a night dive (make sure to take your flashlights along) and that was fun. I don't feel like we saw that many cool things other than a 'family' of 3 small rays and we did do a light turn out to watch some phosphorescent stuff float up. Hearing yourself breathing and your bubbles and being totally neutral and in the dark was soooo soothing. Fastcar was our guide most of the week and Violet in the dive shop was a super sweet lady.
We did a few offsite activities and never once felt unsafe. Skip the horseback ride and swim. It's not a swim, it's a walk around in the water on the horse for maybe 5 minutes. The horseback ride part was ok. The kayak and canopy tour was fun. The shopping tour was to a small gift shop/liquor store (you can get appleton rum in the states fyi), then to a very expensive small strip mall with jewlers and some clothing places, and finally a 15 minute stop at a 'market.' The market were local craftsmen and women. I wish we'd been able to find another area like this that was larger and could have stayed longer. By the time we got there, we were rushed around. We did spend a bit at the market, and they do love to bargain! Make sure you get cash before you get to the airport/resort to tip the luggage handlers and since your resort may not offer an atm.
No Pharmacy Reps approached us beyond the beach, but they do offer necklaces and other items. If they bother you, just walk away with a no thank you.
Also, when you ride around to the offsite activities you can see how poor that area of Jamaica is. I'm not sure if the entire island looks that way and can't pass judgement on it.
As for being a single diver, the crew like to get in the water also and I'll bet if you asked one to buddy up with you they'd have no problems.
I hope you each enjoy your trip as much as I did. I would go back again, but maybe to another location. Why not start at the bottom and move toward the top?