I did the Oceandancer earlier this year (end March / start April) and it was a pretty amazing experience. Never seen so many mantas in one single dive. I kid you not - perhaps 30 individuals - all huge - all v. close. Saw a large whale shark (this happened to coincide with my birthday!) which was interesting but poor thing was getting pestered by all the snorkelers. Overall, the diving was top notch, lots rays, mantas, sharks (white tip reef), turtles, lots morays, tuna, and all the reef fish. Boat was nice - crew friendly. Food good - but more a 'sit down' restaurant type thing than a get up and help yourself. On the explorer boat (Bahamas) there wasn't any way a crew member was going to come over, unfold your napkin and then place it on your lap! (nor do we really need that - but there you go).
If you have any specific questions - fire away. (can only answer relative to Ocean Dancer)
TJ