Opeth will probably never be "mainstream" in the sense that they will be on the top 40 billboard charts in america, or book 10,000 seat venues worldwide and have a relentless and huge fanbase internationally and be millionaires...in fact, id bet a lot of money they wont. However, Opeth could be considered mainstream in the sense that they sell more records and are more "accesible" than most underground metal acts....
Lets keep something in perspective here Detric and others...Opeth arguably sold out during the Blackwater Parks release...which i find ironic, because that was the album many many Opeth fans even heard about the band from. I myself was shocked at how the fame of the band took off at that point (i knew very few people into them before that). I figured that was the point when Opeth hit the big time in the metal world, and i felt somewhat confused about what to think of the band at that point...that many of you i guess are feeling now due to damnation and deliverance. But i realized it was a good thing (not that i really cared in the first place, just found it interesting)...my only real concern with Blackwater park was the slightly less interesting songwriting than on the previous records.
That being said, i think it does come down to the music and you personally. Anything other than that should be written off as immature, dilluted, fantasy world, nerdy fanboy syndrome...and stopped immediately. Have your brief grievances about the "death" of your beloved "underground" metal band, and either adjust to their not so newly found and frankly WELL DESERVED popularity, or move on and start listening to some mediocre band like Kalmah, drawing horns on the pictures of mikael in your Opeth scrapbook and crying yourself to sleep every night, until you decide theres no reason for you to live and you decide to blow your brains out.
in other words...grow up douche.
