I actually don't mind it being fun but forgettable! I like being able to watch a fun movie that doesn't DEVOUR MY SOUL for months. And it did a really good job at being fun. But it... didn't really have anything else to say, I think, and none of the characters really had any personal stake in the plot - like, Gamora *should* have had personal stakes in the plot? But they never really let her do enough to sell us on it (I actually found myself siding with Nova in the Gamora/Nova fight, because we actually understand Nova's motivation - survive until you find someone powerful enough to kill Thanos, which is a pretty relatable motivation - in a way that Gamora's never really coheres.) Drax sorta has a personal stake except that it's just manpain, so, whatever. Quill and Rocket and Groot don't really have any personal stake at all.

Which is fine! I wish we had more action stories these days that didn't require everyone involved to go through wrenching personal crises every week - that's part of what made it fun, that the motivation was people doing good things just because they needed to be done and they wanted to help their friends, yay. And I really like that Quill's relationship with the pirates, for all its fucked up ness, didn't end up defining him at all, it was just another sucky thing in his life. But admittedly doing awesome stuff with no massive personal stake doesn't make for the kind of story that sticks you hard where it hurts.