I've been listening to this album for about 19 years since I got a cheap cassette version from the bargain bin in HMV. And it's not bad. It's not a great album - not a great Clash album anyway - but it's still listen-able, and gets better the more attention you pay to it.
What's good about it?
Joe Strummer's lyrics, of course. It's just about the only thing that tries to describe England in the mid- to late-80s and paints a picture of it as the real horror that it was. Greed, Thatcher-Reagan, Cold War, Miners' Strike, acted out to a soundtrack of awful soulless pap and Gary Davies. Listen to North and South or Three-Card Trick, if you can make out the words, or the song that should have been the title track: This is England. Joe Strummer slipped off the edge of the world in the previous album with Straight to Hell, and here he is in the Underworld. The album conjours up the dreary, suburban, concrete ennui of the film Meantime. Not a lot of fun, but something real, at least. Strummer doing what he did best - struggling, and trying to put the struggle into words.
What's bad about it?
The music, of course. Not that underneath the heavy-handed production there aren't some hummable tunes, but with the loss of Mick Jones, the Clash (or Strummer and Bernie Rhodes at least) lost confidence in the band's ability to 'do' music. Get a hold of the live versions of these songs and you'll hear this could have been the most consistent, rooted album that the band had done since their debut a decade earlier.
Or think of it as the first album of Strummer's solo career.