When they first started expanding the CL it made sense, then the money just got too big. 20 years ago a meeting between two big clubs in one of the european cups was an event, something you looked forward to. You didn't have the amount of coverage you get these days, where you can follow all the big leagues live on television or on the internet. Players move between the leagues in much higher numbers, there just nothing exotic about it anymore.
There's no fun in watching the same teams play each other season after season, you have your domestic league for that. And there's absolutely no fun watching the top clubs fielding weakened sides against some minnow. That's what has happened to most leagues across Europe, they've become minnows. There's no chance of getting any real upsets anymore. You need to fudge up monumentally to not advance from the groups if you are an established CL contender, though United seems to manage it from time to time. By the QF stage it's usually down to the select few: Bayern, Lyon, Inter, AC Milan, Barcelona, Real Madrid, Chelsea, Manchester United, Arsenal. At least 5 of them have been in the quarters for the last 4 seasons, before that you'd regularly have Liverpool and Valencia.
The only solution for me is to reduce the CL. League and Cup winners from the biggest leagues, league winners from the rest. It will give domestic cups more status and it will improve the Europa League as well and make for a more even distribution of money as you won't have the same teams taking up the spots every season.