For anyone contemplating a Series S, I've had mine for just over a month now and think it's a cracking little console.
Went for the Series S as I'd describe myself as a casual gamer - the console is used mostly for video (Netflix, Prime, Plex, Kodi etc) with the occasional bit of gaming thrown in. Didn't want to spend too much and the Series S ticked most of the right boxes. The biggest draw, for me personally, is the considerably faster CPU and solid-state storage. Previous-generation consoles were behind the times in those regards (even the PS4 Pro and Xbox One X resorted to hard disks) and I found the ridiculously long load times off-putting.
With Series S a lot of those admittedly first-world problems are alleviated. Find myself able to have a quick game of something during the half time break, because games load so fast, or even instantly in the case of Quick Resume. I like the fact that the console doesn't consume that much more power, it is practically silent all the time, and it's so small it fits into the media unit with no hassle. I did wonder if the 500GB storage capacity would be a problem, but that isn't the case yet; I've already got more games downloaded than I'm likely to play in a year and there's still a good amount of space left. The console turns on really quickly even from a cold boot (no need to waste power on standby), downloads ought to be smaller and faster without the need for 4K textures, and the new joypad is really nice to handle.
In terms of downsides, I'm not overly keen on the new USB-C charging cable as it doesn't have a light to tell you when the battery is full, and I reckon the Xbox OS could do with sprucing up. Though the UI is familiar and easy to get around, it's starting to look and feel a bit boring.
As for the games, I'm quite enjoying playing older titles that I missed on the last-gen due to a lack of patience. Couldn't abide the load times so it's nice to be able to revisit games and not have to sit around waiting for what feels like an eternity. Managed to get a really good deal on Game Pass and finished Ori and the Blind Forest last weekend. Tremendous game with an incredible visual style and a truly beautiful soundtrack.