I watched this a lot as a kid but now that I'm grown up I see it is heavily flawed but I still like it. The animation, when it's not unfinished, is really good and I am a sucker for villains that want to marry the hero or the hero's love interest.
Now for the flaws. There are moments where animation is unfinished and some parts are rushed like Drake announcing his plan just to reveal him as the villain. Drake's muscular appearance and his obsession for Marina is also very similar to Gaston and Belle from Beauty and the Beast.
Also Drake's minions are very unneeded. There's his three goons that were similar to the Three Stooges and served no purpose to the story. There were also those buzzards that Drake called his servants that only appeared in one scene. Also near the end of the film it's been stated Drake kidnapped Marina, but then why was she staying at Drake's lair in the first place? These confusing plots and twists ruin what can and should have been a very good movie.
However we do have an answer for this. Changes demanded by MGM made animation fall behind so Don Bluth and Gary Goldman left production and demanded to be left out of the credits after seeing their work ruined.
Overall I would say this movie is at least worth a rental.moreless