In regards to the plot being a mess, mmm, it wasn't the tidiest I will say. I did feel like for my friend and I watching it, having seen all the other movies more than once, and having a fair bit of knowledge about the Marvel universe it was ok. But for just a general movie goer, who may not have seen all the previous movies, a lot of it really would make you think "wtf"
Some random thoughts (most are a bit negative, not that I didn't like the film but they're just sticking out)-
-Thor's whole "journey" did seem a bit of a waste looking back. Kind of setting up Infinity Wars and (I presume) Thor: Ragnarok, but as a whole in this film it didn't really go anywhere.
-Was it really necessary to have Idris Elba & Hayley Atwell's names on the poster? I'd rather have had their appearances be a surprise. Same for Anthony Mackie really.
-No real explanation of how Tony/Iron Man came back after the end of Iron Man 3, he just was.
-The New Avengers scene was awesome, Scarlet Witch looked
hot. But it would have been nice to have had a little cameos from maybe Ant-Man, Dr Strange, Black Panther etc, but I understand if they wanna save them for later.
-Hawkeye's thing of "I've been possessed. Not a fan" was awesome

Some really nice stuff for him to play with in this movie. Although if he had a wife and kids I don't really get why Black Widow was wearing an arrow necklace in The Winter Soldier then.
-Baron Von Stucker... so he didn't really do much huh?
-It'll be interesting to see how Agents of Shield intersects in its remaining Season 2 episodes then. I presume a lot will be at the start with Dr List, and it'd be nice to see Von Strucker, seen as he did naff all in the movie. And when Nick Fury showed up at the end saying he brought some old friends, I was
really hoping to see Coulson on that helicarrier. Alas
-The mid creits scene was a bit too "blink and you'll miss it." Again, this is that thing of hardcore fans enjoying it but average movie being left clueless.
We all know the glove has a tiny cameo in the Asgard vault room in Thor 1, so we know that's where Thanos was. But most of the "norms" won't know that, or know that's where it was supposed to be. They could have at least made that scene a little longer, establishing that it was Asgard, see Thanos break in etc. That's my problem with the MCU movies- I enjoy them, but they all come across as so damn rushed.