Difference between kitkat 4.4.2 and lollipop 5.0

Am going to upgrade my F350L 10 d to F350L 20b , vis LG PC suite , and need to know:
1- What is the advantages of Lollipop 5.0 and the 4.4.2 ? Does it worth ? any disadvantages ?
2- Is tehre a way to go back to 4.4.2 if I need to ?

Thank you all.