No doubt I'm going to be called a troll, but if we equate "better" with "more successful," then I can answer it:
-Broad, low brow humour that suckers in the majority of its target audience. Broad enough to appeal to all ages (seriously, I work in a library, the amount of Marvel stuff that's sprung up in the kid's section is to the extent where it has its own box), but not offend anyone.
-Playing it safe. You might call this "consistent vision," but it's a vision that's dictated by company suits rather than a writer or director. Even people who like the MCU have noticed this, that there's a 'sameiness' to MCU films. People know what they're getting, and will go to get the same product over and over (compare Avengers to Guardians - "bunch of people who can't work together must band together to save city from invading aliens who's using a McGuffin in said invasion, after which they're all friends and have their own rocket ship"). It's the same reason why I found The Force Awakens offputting, in that it riffs off A New Hope. Apply that to an entire movie series and call it a virtue.
-Duality: As in, the good guys are good, the bad guys are bad. I've gone on about this elsewhere, but I can't name a single MCU villain with any depth (people will cite Loki, all I can say is "daddy issues"), and certainly not any with anything approaching moral ambiguity. Aldrich is the only villain I can mention who's engendered any level of sympathy from me, but this is a blip in the realm of "take over the world" (Red Skull), "destroy the world" (Ronan), or "destroy the universe" (Malekeith). But as I mentioned in point 1, "good guys vs. bad guys" is easy to market.
-Continuity Porn: Another positive for some I guess, but the MCU is, by definition, connected. And when everything's connected, that gives a drive to see things that you wouldn't otherwise watch. Suppose I liked Thor, for instance - well, all intents and purposes is that to see Thor: Ragnarok, not only would I have to see the previous two films (which is a fair request), but at the least, the Avengers film (to understand who Hulk is, since he features in it), and arguably, even The Incredible Hulk itself. That's three films I have to watch to understand a character who, for all intents and purposes, is from an entirely different movie series to the series I'm theoretically watching. Like I said, I accept that this is a plus for some people, but it's part of the reason why I've given up trying to follow the MCU. Guardians I enjoyed, and likely in part to its stand-alone nature, whereas in Iron Man 3 (my favorite), I still would have to have watched The Avengers to understand what "the Battle of New York" was, and why Tony was freaking out. Fine for people who like this thing, not fine for someone who only saw The Avengers by chance, and wouldn't have seen it in preparation for IM3, because I'm sorry, I don't care about the other heroes, I just care about this one.
-Faithfulness of Adaptation: To some, this is a plus, that MCU has produced faithful adaptations of the source material. Fine, I can accept that. I can see that being an inherent pro. That said, I don't think that's an inherent virtue. Plenty of film adaptations (Lord of the Rings, Starship Troopers, The Shining, Howl's Moving Castle, etc.), differ siginificantly from their source material in key areas, if not in their entirety, yet are all lauded. How well a film adopts its source is academic on how it works as a film. To use one of the above examples, as an adaptation, Starship Troopers is terrible, to the extent that it's pretty much anti-book (as in, the opposite of the book it's based on). As a film, by itself, it's a good fun sci-fi/action flick with likable characters and niffy sattire.
So, yeah. Flame away. But as someone who's seen 7 MCU films, liked 3, and can only call 2 good, the pros that people cite have usually been cons, but I can accept that they're what draw people in.
