That's kind of a stupid question... (a good, but stupid one). Well, I can't say all the reasons why I love them, just because there are too many. I'll try my best though:
-Jaska is one of the best drummers I've ever heard (aside from John Bohnam).
-Alexi and Roope/Alexander are the few greatest guitarists.
-Henkka is the greatest bassist.
-And Janne is the greatest keyboard I've ever heard!
-Their music has their own sound, rather than sounding like everyone else.
-Alexi has the greatest vocals I've ever heard...
-I just flat out love the whole band...
Man I can't name everything... are you kidding? It's impossible! (If anything, it'd take at least a month to write everything)!