The Mars Volta always kinda reminded me what Yes would have been like if Jon Anderson were into opiates instead of hallucinagens.
And yeah, I agree with the general consensus that there's a plummet in quality after FtM, obviously. I like Frances and Deloused very much, but they've been off my radar since Amputecture disappointed me tremendously. Every once in awhile I'm encouraged to give Bedlam or another newer TMV record a try, and I usually find it to be better than I remembered, though still not go.
This is still kinda a weird moment for me. A record store clerk encouraged me to check out The Mars Volta right when I was getting into progressive music, around my sophomore year of high school. I'd already discovered Tool the year before, and that'd led me stuff like Pink Floyd ironically. I was buying my first copy of "Dark Side of the Moon" when the clerk handed me "Deloused", which had just come out. He gave it to me for like $6, which must have been all I had. Anyway, I took the album home, popped it in, and was immediately blown away.
"Frances" didn't really impress me as much when I heard it a few years later. By that time, I'd discovered even mroe great music: dredg, Dream Theater, Yes, and so on. I was starting to sense that TMV's sound was more than a little bit derivative, and that compared to other stuff I was listening to, their music seemed to contain hefty amounts of fluff and incomprehensible white noise segments. I did get into "Francis" eventually, though, always willing to be challenged by new music.
By the time "Amputechture" and "Scab Dates" came out, I just didn't care. The former record sounded burnt-out, and frictionless. "Scabdates" was a joke: the first time I ever felt legitimately ripped-off by a record purchase from a band I liked. I was really excited when I heard the 4 song teaser from "Bedlam", but that excitement disappeared when I realized those four songs would be the best on the album.
After that, I discovered enough new music that I just didn't care about following TMV anymore. But, it's still interesting. One of the first bands I got into and one of the first I feel like I "discovered" right from the beginning are now broken up.