Well, generally i like the epic legnth of Opeth's songs. But Dirge for Novemebr could of been 234038413713893.... times better and more effective if they would stop repeating it soooo bloody much. I mean, the riff's very drowning and the acoustic lines very beautiful and hypnotic, but they don't need to play each idea 3 minutes, i guess they didn't want to do another Leper Affinity or something. But oh well, Opeth still (generaly) slay with their long songs.
Metallica and Rush got me into the long song thingie when I was very young. I've always just loved music so why want it to ever stop? Then came Floyd and Zepp improv that lasted 15-20 mins that really got me into the lust for long songs. Opeth seemed to fuse 70s prog and metal effortlessly and thats why I love them and their long songs so much. MAYH doesn't seem to have short songs because they all seem like one huge song to me. So I think the longer the better and throw in more solos while your at it. Mike never writes shitty solos or just fillers so work in even more!!