First of all, Oceanborn is a huge step when thinking about Nightwish's debut album, Angels Fall First.
All the elements of folk music and ambience are forgotten, and instead Nightwish have concentrated on using Tarja Turunen's wide voice and playing pure heavy metal.
Or, well, another description could be opera metal.
Drama and a variety of melodies are used and effective, but overrule all expectations.
Songs are catchy, but they have a long lifetime.
Also, the whole band does great work: even though they seem like another Dream Theater-wannabe, Holopainen and Vuorinen use their instruments with patience and don't slope into unneeded tricking.
So everything seems to be alright, but the album as a whole lacks a little bit of diversity, and sometimes falls into repeating itself.
The songs are, however, very strong, and the album as a whole works great.
Oceanborn is, so far, Nightwish's most successful album.