I think with the seeding pots nowadays, it takes away the chances of a shock result, it's all geared towards having the better, money making teams in the latter stages of the tournament.
Bring back a straight forward knockout cup - even if each round is over 2 legs - it may give us some excitement when you see some little unknown team from Hungary taking the mighty PSG or Barcelona to extra time or penalties, never mind the euphoria if they manage to knock them out on their best day ever!
I've attended many, many games over the years - and that buzz of it being a knockout game, thats what keeps you on the edge of your seat.