IN MY OPINION: Pohnpei is the "sleeper" for diving in Micronesia. Compared to Truk, Palau, and Yap, very few divers go there. They should. There is a very good choices on types of diving here, from 2 sites with mantas, 3-4 with very good reefs and walls, and one of the best wall to wall sea fans dive sites tht I've ever been on.
Like most other divesites in the region, the divesites that are inside the fringing reef don't have the best visibility, so consider 30-60 ft as the norm. Outside reefs are 80'+.
Ant Atoll, outside the main island of Pohnpei, has a winding channel dive that can stand up against any drift dive, anywhere.
The land attractions are waterfall hikes (must do), and of couent ruins at Non-Madol.