All of their albums are good,next you should probably go for Mandrake,which was the album before Hellfire Club and is generally rgarded as their best work.There is a compilation album called Hall Of Flames which covers everything before Hellfire Club.The album you are asking about is called Tinnitus Sanctus and is a solid listen but a bit less commercial than the other more recent ones.Hope this helps,don't forget to check out the Avantasia albums also which is Tobias's other band and contains lots of guests on each record.