Every band I've heard described as 'like Opeth' has always been dissapointing. Most of that is the greatness of Opeth, so I've given up trying to find another one of them. Instead I'd check out bands that, like them, think on a different plane, although are in different styles. Arcturus, Agalloch, Ulver (keep an open mind), Solefald (1st or 4th album), Enslaved (check out 'neogenesis' off their new album), and particularly check out a new band on The End records called Subterranean Masquerade (most similar musically to Opeth of these, but lighter and more 'avante garde' for lack of better terminology).