I rolled my eyes when they fridged Black Widow in almost exactly the same way as Gamora. It was a big mistake and I don't like how quickly forgotten her death was. She was pretty much the first and, for quite a while, only female hero in the MCU and they brushed her aside in a terrible way.
I also feel, strangely enough, that despite the long runtime, the film felt REALLY rushed. They could have added a few more scenes in the second half to help the pacing. I also don't think this film really did much to assuage my issues with Captain Marvel either, she's still unrelateable and a bit of a personality vacuum and she's far too powerful with no real weaknesses. I was surprised by how little she was in the film but I didn't miss her which is a bit of a worrying sign given that she's likely going to lead the MCU going forward.
My last complaint was that they played it too safe, I liked that they didn't undo the timejump (although that makes Spiderman's situation odd, did every one of his supporting cast get dusted with him? 'Cus his friends would be in their 20's by now if they weren't), but I felt like they could have taken more risks with the plot. I think it's a shame that they completely undid Thanos' characterisation and journey in Infinity War as well just to make him more of a moustache twirling villain when he was more complex before.
As for what I liked, I loved how Cap and Tony's stories ended, it felt right and deserved and they did right by both of them (I just hope they don't undo both of those endings down the road). I teared up quite a bit when Tony reunited with Peter and during their last goodbye, I loved their relationship and it's one thing I will miss going forward.
I liked how (although it felt a little forced in some ways) the female heroes got their chance to shine as well, I almost went full on 'yaaaas' in the cinema when Scarlet Witch was beating Thanos' ass. I just hope the scene where they all teamed up is an overt tease for an A-Force film. I think one thing they did well in this film was that almost everyone had their chance to shine which, for a cast this big, is a big ask.
I thought the final battle as a whole was just perfection and I loved the whole 'time heist' part of the film. I thought the first half of the film was great tbh and I wished we saw the effects of Thanos' snaps in places like Wakanda which was obviously left without heirs as both T'Challa and Shurie were both dusted.
As for the future, I'm looking forward to Guardians 3 being rebranded as Asgardians of the Galaxy and I'm glad they've found another trilogy for Thor to find a home in as they only made him truly great in Ragnarok and it would have been a great shame if his story ended just as they had finally found out how to make him work well as a character. I also think that one thing they'll announce soon is a Young Avengers film, the stuff with Hawkeye's daughter and Cassie remaining a teenager felt like an overt hint, as did the lingering shot of that teenage boy at Tony's funeral. If a Young Avengers film happens then it could be huge for diversity since two of it's most notable heroes are gay and in a relationship and it would probably be difficult to do YA without that aspect since it would piss a lot of people off.
Beyond Asgardians of the Galaxy, A-Force and Young Avengers though, I'm not sure what else they hinted at. I was half expecting a tiny X-men hint but it's probably too soon for them yet.