I think it's an above average controller in terms of features and quality, with an above average pricetag.
For people that want something good for PC, it's a great controller to consider if 99$ sits in your price range. However, traditional controllers often work with multiple ecosystems whilst the steam controller notably does not work well as a controller outside of steam.
For me, it's a worthwhile purchase to get one standalone and maybe a second one later when it's bundled with the other steam hardware. At 99$ I'm definitely not buying 4 or even 8 for couch co-op. My buddies will have to BYOD or deal with the drawer of old k400's.
@ ~17:30 in the GN video "the controller acts as a trackpad and keyboard without Steam running". It appears to not support DInput or XInput so any emulators or other storefront game would need to be manually added to Steam to be able to use this. Such a shame, for me this went from instant purchase to let me get some TMR replacements for Dualsense. I hope they can change this in the future.
Valve has made its $99 Steam Controller official with an actual release date and early reviews have started coming in. Gamers Nexus has tested various aspects of the controller and found it to be quite impressive.