If you liked City of Death, then Shada is definitely worth a watch as it's very similar but still an intruiging watch on its own terms: I think it's such a huge shame it was never completed as it could have been a standout of Tom Baker's run. I honestly believe Season 17 would have been much more popular if this story had been included to finish it off.
Like City of Death, Shada is often very daft in your typical Douglas Adams way, but clever in its own little way too. There are some really interesting ideas such as the character of Professor Chronotis and the titular Shada itself... and as usual with Adams, chemistry between characters is very unrealistic but fun.
It's not very long, most episodes fall well under the usual runtime of a Classic Who episode, but I would say it's certainly worth your time if you're interested as it's the gem that never was.