Length isn't important. Well- that's what they say, but I want to tell you-
Deep is irrelevant, especially on the South side of Roatan.
The best stuff is shallow.
I have logged a few dives in the Bay Islands and I have seen darned near 85% of the Humann/DeLoach Fish/Critter/Coral ID books
without going below 45fsw.
Fantasy Island, as mentioned above, is on the South side of Roatan. This is an area that is quite unique in the Caribbean. the reef walls begin their vertical drop in very shallow water. The depths of the "break" on the South side reefs are from 3~45 fsw. The first sand flat is often found at about 95fsw. I have logged maybe 170+ dives below that level, and I have seen very little to recommend it. If a DM or expert wants to show you something very cool that is of a sedentary nature, if you are capable and comfortable with it, if you advise your DM of your intentions, have at it.
Otherwise, the cool stuff is above 45 fsw.
Your post was very vague, but the map you hotlinked is of the West and North sides.
Other dive ops from other resorts will access the reefs nearer to them. On the West end, wrapping round to the North, they will take you to dive spots in the 'protected Marine park'. In this area, you will likely see larger fish of the common Caribbean varieties: Groupers, Parrot Fish, Baracudas, as well as Lobster and Crab. On the South side, critters of this size will be less plentiful, but you will likely see them. Dives in this N&W area tend to be deeper as the character of the reef puts such interesting stuff deeper.
Back on the South side, you will be shallower, but you'll be seeing Pipefish, colorful camouflaged miniature Crustaceans (both Shrimp and Crabs), and lots of juveniles of the species hiding in the intricate reef structure. Just as the big storms strike to the North and west, the South side is the protected side- where the shallow wrecks are and where the florid reef is. In that the wrecks are shallower, you can spend more time on them, and they have a lot more life on them as critters depend upon sunlight. You get a lot more when you are shallow...and axposed to the Southerly track of the sun.
This shallow reef runs from Mary's Place then East to Port Royal. On the way, you'll go past the Yacht Club, Subway Watresports, Fantasy Island, CoCoView, and the Reef House to name the major players. The North side is services by Anthony's Key, bay Islands Beach resort, Inn of the Last Resort and several day-dive ops.
I may have left some out. i'm old and have a lot of Nitrogen in my brain
Most everyone gets to dive Mary's Place, which~ although it is the "trademark dive" of Roatan, it really is only a long deep crack through a reef. After many, many dives there- I was recently taken through by a world class expert who had done Mary's Place some 400 times.. She showed me 1 unique critter inside of it, 1 ten feet after the end, and that was it. We spent the rest of the dive poking around the shallows and found tons of cool stuff.
Stay shallow, see the cool stuff. Perfect your buoyancy, take a class. Pick your DM well, stay with them like a magnet. Bring a small flashlight and be ready to hand it to your DM. many times I have looked at what he was pointing at and still unable to see it. A flashlight really helps. If your dzm isn't showing you at least on e SeaHorse each day, politely change DM's. If he feeds fish in any way, this should be discouraged. Some DM's do this very discreetly, but if you see a pack of fish following your DM- this is what he is doing- as well as impressing you with the numbers of fish he showed you. A good man uses simply a sharp eye.
There is no need to go deep.
