You know, I use to love really hard stuff like Dimmu Borgir, but now I almost can't stand it.  I can't really explain the change, it just grinds on me.  I much prefer acoustic or a very clean, stylistic electric guitar piece.  Power chords and fast drums just don't do it for me anymore.
That being said, I still like a lot of Opeth, and I find the Blind Guardian and Rhapsody are still listenable, mainly because I like Blind Guardian's choral style vocals, and I like Rhapsody for the vocals, but also for their incorporation of orchestral instruments.  I don't like all their songs though, just the ones that have those elements.
To illustrate my point, here are a couple of videos that I find very enjoyable:
Opeth - Harvest
        
    
Opeth - Windowpane
        
    
SymphonyX - Accolade II
        
    
The Tea Party - The Bazaar
        
    
The Tea Party - Angels
        
    
Brad Sucks - Fixing My Brain
        
    
Regina Spektor - Us
        
    
Ok, so that last one was piano rock, not guitar.  And a female singer.  But Regina Spektor is freaking awesome, so it's all okay.
                
                
                    Marsz, marsz, Dąbrowski,
Z ziemi włoskiej do Polski,
Za twoim przewodem
Złączym się z narodem.