Install the Android 4.4 experience on mostly any Android now:

There are just a few steps for this. If you have an HTC One, you will lose (or happily get rid of) "Blinkfeed". You will get new or renewed apps/services (search, now, photos etc).

Step 0 - Before starting you have to go to settings, and find “Security” -> “Unknown Sources” and check that box to allow installation of apps from unknown sources.

Step 1 - Download, unzip and place these 3 files on your phone. Then install in this order:

     1 - PrebuiltGmsCore.apk
     2 - Velvet.apk
     3 - GoogleHome.apk 

You can then run the new "Launcher" from your apps and set it as default when prompted to do so.

Additional step: install the new Hangouts+SMS and ani-gif support. Get it on Android police, here:

http://www.androidpolice.com/2013/10/31/apk-download-hangouts-1-3-support-sms-animated-gifs-location-sharing/

I for one am enjoying this new Google experience.