Annoying thing about Opeth

For me, undeveloped repetition is what's really boring (like with Amorphis, for example). I'm not bothered by that too much with Opeth, although, Mike does seem to like repeats as a compositional tool. It works best when there's some sort of variation in the repetition, either in dynamics, instrumentation, lyrics, rhythm, or the addition of fills from the various instruents. Repetition for the sake of itself reeks of padding. And as a means of creating tension...well it has to be the right musical material. Repetition alone doesn't create tension just as it was pointed out, and I agree, that it doesn't create atmosphere.
 
Sections that I've been told are too short:

1) "Am I like them" from "The Night and the Silent Water."

2) "Devious movements in your eyes" from "Bleak."

3) The instrumental, Castlevania-esque section near the middle-end of "Baying Hounds".

4) "Your memory's nothing but the scars on me" from "Deliverance."

5) "Making my way through... something... oh-oh-OH" part from "Godhead's Lament" (sorry, can't remember the exact lyrics at the moment, SL isn't one of my favorite Opeth albums).

And many others.

In fact, one of my friends told me that Opeth should've made ENTIRE SONGS from these sections alone.

I don't agree, but then, I don't really agree with you, either. I'm in the middle. :D

Speaking of making entire songs from sections, the end of Heir Apparent could be it's own song.
 
IMO, the repetition in Opeth IS needed in all songs. It suits all the songs perfectly; for me, it sets up and creates the atmosphere/makes up the mood of the song, like in Wreath or Deliverance. Or, just lets you "get into it" like one of you said; a good example of this would be In Mist She Was Standing.