Asimov's Mysteries was the first book I read, over 30 years ago now. I grew up on Asimov and he will always be my favourite SF author. That being said, when I first bought Foundation And Earth, I was very disappointed. This week, I re-read it to see if my opinion had changed in a decade.
The thing is, there are some great ideas here and some Asimov magic up there with anything in the original Foundation trilogy. The encounters with the feral dogs and with Bander are classic Asimov - tightly written and flowing.
On the other hand, there are pages of repetitious argument between Trevize, Pelorat and Bliss, none of which advances the narrative. Nor does it bring any new insights to Gaia / Isolates. It truly feels like Asimov is padding out the book. It's certainly not as gripping as Foundation's Edge.
BUT if you're an Asimov fan as I am, this book is an essential read. And when the trio meet the final new character it did bring a lump to my throat. The way Asimov weaves together his stories into the one timeline is a joy.