The old format had a total of 96 games in the group stage and at the end of all that, 50% of the participants (16 out of 32) were eliminated. The new format has a total of 144 games in the league phase and after they are all played, only 33% of the participants (12 out of 36) are eliminated.
The new setup just feels bloated and ungainly with
less jeopardy than we had before. I've said elsewhere that there will still be seeding to play for in the last games amongst teams that have already qualified but I'm not so sure that's going to be such a huge factor now.
UEFA's primary goal seems to have been to substantially increase the total number of games so they can sell an enhanced 'product' to the broadcasters.