I don't like 8.1
They way they did the Facebook integration is ridiculously slow. I used to be able to tap a contact, swipe once and see their FB/Twitter activity, now it's nothing for Twitter, and extra tap and slow wait for FB. Like I see what they were trying to do with all of this but the actual execution is bad. FB contacts refuse to show in the contacts list.
Skype is slow as hell, and shocked that it isn't baked into the OS. Should be.
Sliding from the top of the screen for notifications basically eliminated the need for a live tile. Would like an option to group like notifications from the same person/status/app.
Internet Explorer got worse. When navigating these forums (refuse to use the horrid app) it has to load like 4-5 times when in vanilla WP8 it just did once. Overall slower.
Wifi took a hit with signal strength somehow.
Seems like MS gets a vision, then back away as far as possible from it, they did it with Xbox One, did it with W8.1, now WP8.1, this seems less like Windows Phone and more like "Hey, lets do what everyone else is doing to try to appeal to the masses" and ended up a sloppy, disjointed mess in the process. I wish the T899M had a GDR3 ROM I could flash to.