Name that RPG

I played a brilliant RPG once on pc or maybe 360 that the rest of the internet thought was only about 5-6 out of 10. It was a third person hack and slash but about a third of the way in you gained the ability to morph into a dragon and it made the whole thing ridiculously good fun, cannot find the fecking thing now, anyone know what it was?

I remember attacking an old galleon lying on its side on a reef, a big island that was all one big puzzle run by a mad ghost, a huge tower on some cliffs that would kill you if you flew near it in dragon form, dont know what it was called but it was an overlooked classic.