My impressions after 1 day...
I love the built-in app updates - more are supporting the extra large tile that shows a lot of useful information.
Mail has a new, cleaner look. I like being able to hide rarely used folders and favorite the ones I care about.
The Newsletter filter in Outlook.com/Hotmail is pretty slick too.
Finance App lets me put in a watchlist that shows on the new larger tile.
Music is finally a good app. It was much improved in the 8.1 preview. Performance is even better now.
Reading list is excellent!
Wifi still doesn't immediately see the hotspot from my Lumia 1020, but it will now show up eventually if you wait a bit.
I still don't get what is special about the hotspot that comes from my phone vs the other hotspots that it sees instantly, but at least it works now. Previously in the preview, I would have to reboot the Surface to get it to see the hotspot from my phone. That is absolutely unacceptable and I'm glad its "fixed".