The Island Bound DLC is a really great addition to the game. It's implementation isn't all that great unfortunately. It doesn't work well with Warden mode, as you can't board ferries as warden, nor can you adjust departure times of ferries and Prisoners searched on bridges can become "unreachable" if saved in such state. These aren't a dealbreaker bugs, they can be mitigated or fixed if they occur, but downplay the overall experience.
It is a great DLC as it adds a whole new layer of possibilities for escapes, it is a great twist to the base game. It greatly expands the options of deliveries and makes water less annoying to build around.
Considering there is no "ok, but could be improved" rating, I'll keep my rating as negative until those two issues are resolved.