It really depends on where you are staying for being able to snorkel from shore. Here on Ambergris Caye, that is mostly true but the MesoAmerican Barrier Reef is very close to shore - less than a 1/4 mile from Captain Morgan's. You can use a kayak to get out there and go fishing or snorkeling without charge. Typically, we go out with a tour to the better spots by boat, though.
Captain Morgan's is an older resort and isn't entirely spiffy with all the amenities you find in newer ones. That being said, the accommodations are decent, there's air conditioning and kitchen facilities (oven and cooktop that are fairly old but no dishwasher), and three swimming pools. There are nicer and newer resorts on the island, but they cost several times as much and this one meets our needs - as a plus, they are not in active sales so no one will ever bother you to attend a sales presentation.
In addition to beach activities and snorkeling common activities here are reef fishing or deep sea fishing, visiting Mayan ruins, etc., not to mention scuba diving. There are a number of restaurants on the island that are well priced compared to other places, although Ambergris Caye is one of the more touristy locations in the country.
Getting here is relatively easy as many major airlines fly into Belize City. Alaska airlines just added a direct flight from Seattle, so there are a number of people coming down from there now. Once in Belize City, the easiest way to get out to this island is by small planes operated by two local airlines, Tropic Air and Mayan Air. It's about a 14 minute flight and quite scenic. There is also a water taxi/ferry system that you can take out from Belize City or Corozal that takes longer but is less expensive; I believe the air fare is about $70 or so last time I looked.
Near this resort there are several restaurants you can walk to and a couple of small stores. The predominant means of transportation on the island is by golf cart, which can be rented for as short a time as 2 hours in order to get your shopping done.
We love the resort, though we've met some long time owners that complain about the changes over the years here. It's pretty easy to find resale contracts here very inexpensively and a 1 BR week costs about $650 in MF currently - we picked up a couple of those and keep coming back. There do seem to be a number of weeks showing up in II lately, too.