Champions league is fine. I would make one change, two at most.
Get rid of country protection in second round. I think it made sense when you had two clubs. But when you have 4 clubs per country in an already economically asymmetric system, it leads to ever more consolidation of power in the big 3-4 leagues. Additionally, it means that very often the same match-ups are generated each year because a number of potential match-ups are excluded. It's no coincidence that we constantly play the same teams each year
Consider removing the away goals rule. Europe is a tiny continent. This only becomes relevant if you have a tie in the Urals. Otherwise, it's a short private jet or commercial flight. You spend as much time traveling as if you took the bus to a domestic affair. It also kills a lot of ties far too quickly. You led 1-0 at home and then make it 1-0 away. All of a sudden your opponent goes from needing one goal to needing three. Piss off.
Making the groups bigger makes no sense. The 4 team group works because at most only the last round is irrelevant. And typically, there is something at stake up until the 6th round of games of 2 or more teams. You put 8 teams in a group, and then you end up with 2 or 3 teams with nothing to play for in the last two to three rounds.
