Two different UI in one OS.
Metro UI and Desktop
for Metro: typical UI you expected that works well with Touch-screens. but KEY-MOUSE is almost a problem. yes simiular to App Store/Google Play, in Metro we like to call. "Windows Store" well lots of useless games/applicated where there still app you know and love from. you know, Where's my Water, Angry Birds (only Star Wars is there), Fruit Ninja, Jetpack Joyride and more. heck even they got a couple of ports. like GTA: San Andreas, Dragons Lair and a couple to choose from. but since you hope to see more of your favortives on Windows 8.1 well http://www.bluestacks.com/app-player.html can solve it for now
(as least you can still use KEYBOARD and MOUSE and Gamepad on all application/games)
for Desktop: Well its the same Desktop you know and love, and the same experience and able to run almost all programs (even Steam, besides not supported but still runs perfect anyway) expect it doesn't have a Start Menu on it.
and one more thing. remember mentioning Resident Evil on Mobile?
well its still there alright. its RE4 iOS version :P