It is so hard to explain why Opeth is "it" for me musically.
There are better drummers, better guitar players, better bass players, better vocalists on an individual level than each of Opeth's band members in the music industry. (for instance, Joe Satriani and Steve Vai are phenominal guitar players). BUT, we're talking about Opeth the band - Opeth the unit - Opeth the complete package!
There is no other band's music that I've ever heard (and Led Zeppelin has always been the band to me, up to now) that delivers a complete musical package like Opeth, NO ONE. I took music classes in college, I went to Berkley College of Music for piano and drums, I've played piano for over 30 years, so I always thought I knew music. Opeth finished the definition for me. They've completed my search for what music should be. Is this to say that in the future I may find some other musical talent that redefines my definition? Personally, I find that hard to believe. It took me 41 years to get here, so it will be a long time (if ever) that someone else comes down the pike and mesmorizes me the way Opeth does.
It's all about the emotion I get while listening to them. I don't think I've ever "casually" listened to Opeth, like having them be background music. My mind could be here or there, I could be physically doing something, but when Opeth is heard, it seems everything around me blurs, and there is Opeth The Music, right in front of me, pefectly focused, taking up nearly 100% of my mind and body.