"Bands that many fans wish would go back to their "older" sound"
Hmmmmm, almost all?
If you look for recent material from....I don't know...Dream Theater, Metallica, Nightwish, Angra, Opeth, Iron Maiden, Yes, Deep Purple and even Rush when the band released their last album (among many and many examples) the only constant among these diverse bands is the perennial complaint that these bands aren't what they used to be.
By the way, IMO this is the main reason why discussing music is increasingly tiring... I understand fans who feel annoyed and displeased, but this endless complaint turns what should be entertainment into something boring.
Evidently this is not true for bands whose sound has always been very similar (AC/DC, Motorhead) and for some bands that decide to go back (in some way) to the sound that pleases their fans.
Some bands returned to their sound in a way that I thought natural (Paradise Lost) and others in a forced way, as a fan service (Judas Piest). I don't have respect when I feel that something was meticulously built with the intention of generating a good reception and not something natural (Edu Falaschi new album is an excellent example).
Of course, this is all extremely subjective.
And let's face it, for some bands it's not even that hard to please the fans. Megadeth is a good example. Looking at the reactions to the latest records, you can easily see that:
- if the album is mostly "fast, heavy and with wank solos" = good (United Abominations, Endgame, Dystopia)
- if it run away (even a little) from what described above = not (so) good (Thirteen, Super Collider).
If Mustaine wants to keep his audience permanently happy, just do anything that's fast, aggressive and with a lot of guitar solos.