Everything is 10x better than WP8, and yes Cortana does work, I was using her earlier on my L520, but you need ot set everything to USA language, region, speech - it's not available in other regions yet
L520 feels like a different phone, extra row of tiles makes it look sweet, custom background wallpapers create an amazing look, screen switching is faster with a much better animation, apps load quicker, the whole OS is a massive improvement over WP8
I was getting bored of my L520 until this update, now it's exciting again, definitely recommend it