There should be two categories here: Worst mix and worst mastering.
There are a number of albums mentioned that I'm familiar with that sound like they were probably fine mixes but got destroyed from poor mastering. Lossy dts and dolby encodes come with the territory so often in surround land (as in the only format ever released for some albums). You have to kind of consider those as more of a preview or teaser for something you truly can't fully listen to yet. (ever?) That Rush Snakes & Arrows comes to mind as an extreme recent-ish example of this.
The batch of DVDA's from around 2000 that had the surround remixes (and remixes in lieu of original surround mixes when originals existed for the title) mostly sound like the crudest cookie cutter intern student made stereo mixes in front. Except with a coldly separated lead vocal in the center with zero reflection support. And then an awkward canned reverb that doesn't match anything blasting out of the rear. That Yes Fragile DVDA mentioned a few times in the thread is one of those.
Speaking of Rush, the surround mix released a few years ago on those "Sectors" editions for A Farewell To Kings was one of the more insulting mixes I've ever heard. Just crude and lo-fi. But that's now been corrected by almost the most accomplished remixes you could imagine.
Lot's of experimentation from the 1970's...
Ya know, it's hard to call some of these bad. (Well it's pretty easy in some cases!) There's a creative playfulness still in some of the bad ones though. I like the experimental attitude better than some of the homogeneous SOP mixes from more recent times.
Really the ones that disappoint me the most are the cookie cutter remixes just cranked out cheap to fill a slot on a disc format that typically features a surround mix with clearly no involvement by the band. Like a lot of the circa 2000 stuff. Then the ones that only get released in the lossy core dolby format as sort of a bonus aside on a primarily DVD Video release.
The most frustrating remixes I've ever heard are the Genesis remixes! Really excellent mixing work throughout with details revealed more than you might have hoped for. Very high level mix work. And then Tony Banks comes in and makes him turn the guitar solos and other parts down awkwardly low. And then it gets the mastering treatment usually done on CD/mp3 versions of releases. Crank up the treble so high you can hear the vocals clearly from an ear bud sitting out in the next room kind of thing. This skewed the mix pretty severely and pushed the vocals up in the center channel over the top of the mix among other things.
Oh, I'm supposed to list 10.
That older bootleggy Rush remix of Kings and the other couple titles that came out around it and then the Genesis remixes. And then the entire circa 2000 collection of remixes I was talking about!
That 10 yet?
Agreed on the poor live mix comment too but with one exception.
Mixing stereo and then just audience in back from multitrack is not the way to go. However, syncing an audience recording in back to a soundboard live recording up front can have wonderful results! (This is more "restoring as best as possible" than "mixing with intention" to be fair.)