I'm working my way through Discworld again this year, up to Lords and Ladies. Such a fantastic series.
I tried a few King books last year (I've read a couple in the past too) and although his world building is amazing they both had kind of damp finishes that put me off trying any others (Salem's Lot and The Institute)
The Discworld series is mostly fantastic. The quality did dip a lot after he got sick though. Which was a shame.
That's the problem with Stephen King. He builds up these amazing worlds and characters. But, the mystery/evil/ghost/whatever when it's revealed can never match what we imagine. Some of his out and out horror books(not short stories) are like that, eg. Christine, IT, Salems Lot etc. You should try some of his other books The Stand, The Tailsman, The Dark Tower. Or take a read of the Bachman books. 4 short stories that are really good.
And I just wanted to get back to you about the Rivers of London series Novels by Ben Aaronovitch. I finished reading them a few weeks ago and your summary was totally accurate. Good start then faded into been very mediocre by the middle and was glad to be finished by the end. The whole dynamic of the magic and the rivers etc didn't work for me. You said you wouldn't put the series in your top 3 urban fantasy series. Same here, I wouldn't put it in my top 3 and I haven't even read 3 urban fantasy series!!
Very disappointed after the good impression the first book made.