TLDR: Waterdeep: City Encounters earns a solid 4/5
This resource is intended for use with the Waterdeep: Dragon Heist adventure but can easily be used for any low-level city adventure with barely any modification (maybe changing a few proper names here and there at most) and any level 5+ city adventure by just changing out the enemies in some combat encounters.
Overall, it includes a TON of solid random encounters full of flavor and intrigue. These scenarios are very well written and feel like WoTC content. You could easily place these pages into the back of the actual campaign's hardcover and it would be impossible to tell it wasn't part of the release - even down to the excellent page design and organization and useful companion map.
The scenarios are divided by which wards of Waterdeep they can take place in (the Dock Ward might have run-ins with rough criminal-types, the North Ward has nobles moving about, merchants try to hawk goods in the Trade Ward, and so on). This is great because sometimes (especially if you only use the official book) Waterdeep can start to feel like one large centralized city instead of a metropolis made of unique parts with their own character. These varied encounters do their best to flavor their respective wards appropriately and set the stage for what kind of area your group is currently in.
The price is kind of steep for a supplimental PDF on this site, but honestly the A-list team of authors and designers that put this together have made it worthwhile. I would use it in any urban module and go so far as to call it a necessity for DMs running Waterdeep: Dragon Heist.
So wny only four stars? Well, unfortunately, this product dropped the ball in a HUGE way that is honestly EXTREMELY surprising for such a well-made resource made by a team of established content creators on this site: THERE IS NO PRINTER-FRIENDLY VERSION. Each one of the almost 40 pages is full color through-and-through, and a good number of them have intricate pictures and designs. Printing this beast will easily take up $30-$40 worth of standard ink and a good hour of time. Unless you have a pdf version on a tablet or laptop (or you want to end up paying the price of a full-release hardcover for a smaller suppliment), this will probably not end up in your DM binder as-is. In addition, the large amounts of ink used for the pictures on top of the page texture will warp standard paper and blur in most desktop printers, so if you are planning on printing make sure you use at least 28 pound presentation paper for the best hold and a high-quality result. For the price, I don't know how this was overlooked. The lack of such a common feature is extra disappointing because otherwise this easily would have been one of the best products on DMs' Guild in general.
[4 of 5 Stars!]