Welcome at MIUI!
I dont want to offend you but its much the same thing every and every time. Always when google releases a new android base immediately the clamor begins that xiaomi should update their roms. After they did the desperation begins...
But did you just recognized that the MIUI (yeah i like that play on words..) is highly customized, so that a change in the base must not necessarily bring a change in the UI?
And beside that, also a thing only few persons recognize, isnt it better to have a highly envolved, working version instead of a mainly public beta with some bugs?
If you want to try something new i would recommend trying cm12 or AOSP, the latter should also be available with an marshmallow base.
Of course i also like trying new stuff, but if you really want to feel the changes you have to use something else than MIUI.
And relating to your new MIUI version, maybe there are no visible changes, but did you mention some performance changes?