Are there any bands like Opeth?

No. If you enjoy progressive death metal, then there are other bands in this genre--although this is a very very diverse genre which is just the nature of progressive musics in general. Some well-known progressive death metal bands include: Pain of Salvation, Death, Atheist, Unexpect, Between the Buried and Me, Cynic, and Edge of Sanity. However, Opeth really is nothing like most of these bands. Opeth's use of harmony and melody really are unique in this subgenre. The band leader, Mikael Akerfeldt, is a huge fan of Porcupine Tree which is kind of similar to Opeth--although, Porcupine Tree would be considered prog rock not progressive death metal.

If you really want to find some good music, check out Progarchives.com. It will be much more useful than me.