Too much gain!
I don't know whether my anti-gain tendencies are because my tastes are changing or because I'm surrounded by high-gain players and am trying to distinguish myself by doing something different.
One thing I know for sure is that it's really fatiguing to listen to bands that use too much gain on all of the guitars, whether they play that way all the time or do the clean/dirty/clean switching that has become a cliche for the nu-metal bands. The heavily distorted parts sound far too close to white noise, to the point where it's hard to hear any tonality at all. In many cases, the tonality has been replaced by rhythmic complexity, which is fine... But if you're going for that rhythmic, palm-muted chunky dull thud, I've gotta wonder why you need a guitar at all...
With Almost Milwaukie, we have one guitarist who never plays clean, another guitarist and a bass player who both vary between clean and dirty (yes, fuzz bass), and me. I'm the only one who plays clean and goes easy on the effects. If I didn't do that, there would be portions of our music that would turn to complete sonic mush. Sadly, my analysis of the quality of the band's sound seems to be a minority opinion of one.
I think you can go a long, long way toward getting a full, heavy sound without using lots of distortion. It's more a matter of arrangement, chord voicings, timing, ... stuff like that. I know there's a qualitative difference between blues-rock players like Jimmy Page, Angus Young, and Jimi Hendrix (I'm conveniently ignoring Jimmy's and Jimi's fuzz sounds, which I don't really care for) and modern shredders who play really, really fast with lots of legato. I make no secret of the fact that I prefer the former.
If I had to make a choice today between a THD Flexi and a Boogie (or especially a latter-generation "Mesa") I'd definitely go with the Flexi. Whereas the Boogies have far too little compression on the clean channel and far too much on the lead channel, the Flexi is nicely responsive over a wide range of gain. My main problem with the Flexi is that I couldn't reduce the gain far enough to get it into tweed territory - it just wouldn't clean up for me.
Yah, I love the tweed overdrive. It does require a lighter touch, but once you get that, the range of expression really opens up.
Tweed amps have all those mids that Fender scooped out of the latter designs. Once they realized that most of the guitar's energy is in the mids, Fender changed the voicing to reduce the mids and clean up their amps at "higher" volumes. That made a lot of sense in the days when nothing (except the vocalist) was mic'd, and also as stage volumes were rising to dangerously loud levels. The need for extremely high volume has all but disappeared, whether you're a bedroom player or a touring pro. Tweed designs - with their early breakup, thick midrange, and detailed response - make a lot of sense for current-day "roots" players. (Although clearly not for the high-gain crowd...)
I love hearing a player bring his guitar "forward" for a solo just by digging in and maybe goosing the guitar volume. The transition is seamless - you can tell it's the same instrument playing a different part. Conversely, when I hear someone kick in a stompbox or a different channel, the sense of continuity is lost.