Been testing Android "L" for a few days now and I have to say I'm impressed. As I've said before notifications really take center stage.
Whether it's on the lock screen or in the de facto notification center they are definitely more robust and that's even without the "heads up" feature working.
The second noticeable thing would have to be the overall redesign. Using a flat modern design Google really took it up a notch. Where Apple chose bright pastels google chose whites, greys and a variation of its accustomed blue color. Much less of an eye sore than that of Apples pastel nightmare, just my opinion there though.
The third but thing I took from my time so far with "L" is the new run time. Fast. That's all I gotta say.
I would be keeping it but as many features that aren't yet working are needed for my trip this week I must "shudder" downgrade.