Most progressive of the 90's?

The term "experimental" refers to something that results from an experiment. The only way to make experimental music would be to create sounds/silence/rhythms/pauses etc. by total randomness, but to do that you have to make the decision to create music that way. Then making this "experiment" has become a composing method, and it's not more experimental than making say, dodecaphonic, stochastic, aleatoric or any other kind of music.

There is perhaps a music style called "experimental music", but experimental music as such doesn't exist. 

This is of course hairsplitting. 

 

Is it possible to establish a difference between being original/innovative and progressive?  Perhaps, progressive is more akin to "groundbreaking", in which case it is a word to be used sparingly (and probably wouldn't apply to many 70s prog rock bands, let alone more contemporary bands).  I would not call Radiohead a groundbreaking band because their albums represent more a contemporary update of rock music. But the way in which they go about is very original and unique and to that extent, they are comfortably more progressive (adj.) than Anglagard or Spocks Beard.

 

But that seems to be lead us right back to prog the genre.  I'd have thought progressive as an adjective implies progressing the state of a given genre of music which Dylan certainly did. Dylan and RS were progressive musicians of their time and nobody is going to dispute that re Beatles anyway.  If we take emphasis on development as the crux of what is progressive, I think tracks like Airbag, Exit Music for a film and Paranoid Android do reveal a thrust on that in the OK Computer album (though there are several more straight up tracks like Lucky or Subterranean Homesick Alien).  It is rightly compared to DSOTM in that sense because that album too has some progressive moments and some much closer to regular rock music.   I agree that Kid A is a more progressive album if taken in that light but I'd then also not dispute Anglagard or SB either.

 

Alt rock is one heck of a black hole ...and in the 90s, it could mean literally anything so what's roughly the music you are comparing OK Computer with here?  In comparison to what the Seattle grunge or Smashin' Pumpkins, U2 or Oasis were doing up to that point, I'd say OK Computer is at a totally different level. It is as intricate and detailed in its execution as Grace but much more evolved and eclectic, formally.  It is as if the band wanted to remind the mainstream scene of the time what great rock music used to be about without sounding like a fascimile of classic rock.  Again, this depends on what we are comparing OKC with it and it's possible there were some alt rock bands at that time who were writing rock music of a lot of subtlety and depth in composition which I haven't heard.

You nailed it there, that's more or less the framework I was thinking of. I agree Radiohead went further than any of the mentioned bands, but I see them as the end of an evolutionary process. They didn't come up themselves with revolutionary innovations, which is the kind of progress we've been discussing here*.  Nothing like what Dylan going electric was for 1965, King Crimson for 1969 or punk for 1976. I just think OK Computer was better, more refined and more accomplished. Another thing to measure innovation with is what paths does it open; or in this respect the innovative bands of the mid to late 90s were Neutral Milk Hotel, Modest Mouse, Yo La Tengo, Wilco, Belle And Sebastian, Trans Am, GYBE, etc., because they were the ones to break the new grounds for '00s indie rock. OK C was an end of the road IMO, that album coudn't be bettered, outdone, continued. Even Radiohead, when they changed direction with the more experimental Kid A and the albums that followed, they were recycling things already done in the early to mid '90s by Pram, Trans Am, Seefeel, Tortoise, Disco Inferno, Stereolab, etc.

* i.e. the groundbreaking revolution implied by the OP 

To make "experimental music" is not about having a method, it is a method. The "experimental" is a method that (perhaps) produces unexpected results, but that is just a way of working. You can of course make music using a lottery machine, and it may generate music that you can call experimental music, but to make music that way is not to make experiments.

As a composer I can normally choose between two methods: 1) pre-determining everything in a work, leading to full serialism, or 2) leaving room for the unexpected development. I always work with the latter. The end product may sound like "experimental", but there is nothing experimental in that working method.

There was a time when anything out of major/minor tonality was called "experimental", which I found tragicomic. From a conservative pop music listener's point of view almost all prog is just what you could call "experimental".