I enjoyed it more than 2016 though 2020 was a lot better. 16-team Euros are still the gold standard.
That's my main takeaway here too - simply far too many mediocre teams. Everyone's disappointed with what the top teams delivered and for good reasons, but at the same time this was actually a tournament that was dominated more comprehensively by exactly those teams than any recent major tournament. Not one of the big teams failed to qualify for the 1/16 finals, and there wasn't much in the way of upsets (or even mild surprises) in the knockouts either. Much of the tournament felt like one team with the onus to win vs one team defending deep with 10 or 11 players and taking their chances on counters. Over and over again. And, more than I think I've ever experienced before, most of the non-top teams just seemed interchangeable - Slovenia, Czech Rep, Slovakia, Albania, Hungary....well organized, 1 or 2 real quality players, full marks for effort, largely the same football. All of them looked competent, none of them felt relevant, or noticeable. '
A short tournament weaves its own narrative, which is to an extent inevitably a false one, making outcomes seem unavoidable or impossible when in reality what we're seeing is to a significant extent coincidence and chance (any single game of football is significantly that, and so a tournament based on single-game knockouts are too). Georgia is a prime example - now being routinely mentioned, also on this thread, as a team with an entertaining style of play. Which really is bollocks - they defended deep with 11 men and took their chances on the counter, just like a dozen other teams at this tournament who will be remembered by no one. We just enjoyed watching them more because they were such huge underdogs, because every player gave it 120% for 90 minutes, because the wonderful Karashkveli was capable of brilliant golden moments and because the win over Portugal set off our "Possible Huge Upset!!" alerts. That win over Portugal (to whom this was a meaningless game) just lined up for us a great storyline that we were more than happy to step into.
Anyway. There are not more teams than before with a real potential to go far. The group stage matters less than before, because it's much easier to qualify for the knockouts (weaker opposition on average, 3rd place qualifcation). The average opposition in the knockouts is also weaker than before, while the knockout stage is one segment longer. All of that as far as I can see puts a premium on control football for the top teams - they are mostly facing opponents they should beat, but who aren't easy to beat. Best route to that is avoiding risk, and trusting that superior player quality will most likely tip the scales their way. Make the probabilities work for you. Unless you can build something truly special, like Spain did, but that is rare. Most tournaments, there isn't a team like that. At the same time, an upset win like Greece or Denmark has also become less likely because the knockout stage is longer. An upset winner mostly has to beat the odds every single game in the knockout stage. Now that's a possible four times rather than three (although depending on the draw).
So yeah, I think there's a case that the format is a factor in making the tournament less entertaining.