perspective from a comic book nerd who doesn't get too hung up on comics vs movies.
I will say this is the FIRST marvel movie that I give a below passing grade to. None of my issues with it stem from inconsistencies with the comics. I'm also not so mad at the casting though I felt the casting of Jolie, and Hyeck didn't help, more just a waste of money.
The real issue here was the horribly lazy writing. spending 3 hours to build up a 5k year back story for characters that ultimately felt limp at best, and didn't do anything to tie the characters to the audience. This didn't feel emotionally connected in any way. you don't feel the struggle of the characters having to watch thousands of years with their hands tied. you don't feel any elation when the characters take a stand, you don't feel any sort of triumph at the end. there are no highs and lows. the whole thing just feels flat. The climax of the movie basically made the whole previous 2+ hours pointless. there was MAYBE 20 minutes of screen time that felt actually needed. coolest scene is basically a still shot lol.