Again, you've done well with this series, but it's got a few flaws.

It had a lot of expository dialogue, and most of it could have been cut done. While that type of thing does help advance the story, you have to strike a balance between that, and the old saying "Show, don't tell."

For example, we really didn't need the last part of Banner's line at 2:57-3:03. It's info we already have, and simply slowed down the scene. Your audience isn't stupid, they know about things like that. Also, this one seemed to have more long talking scenes, and less action, the pacing dragged along and some viewers may have become disinterested.

Now, for being named after the Hulk, said giant was only in the thing for about 20 seconds, and even that felt odd.
It's hard to animate the figure, I know that, but adding in more arm swinging and not just spinning back and forth helps a lot. And what was the point of having Hulk hit the other heroes? Could he have not just left on his own? And how come the villains didn't suffer any real injuries from the attack? I also found his transformation underwhelming. Sorry if this sounds nit-picky, but I'm a Hulk lover.

Also, there are a few flaws with the "Only a handful know about the cube" theory. There were the guys that helped transport it there. That whole Hawkeye thing also seemed really dragged out, especially as it was mostly things we already knew.

Try to speed this up next time, but still, it was well done.