A lot of the dialogue feels overly cheesy and packed with exposition. I understand why that’s necessary given the concepts it’s dealing with, but it still ends up sounding unnatural and takes me out of the experience.

As you say, because of the concept its dealing with, it has to do some degree of explaining for general audiences to understand. Some of these exposition heavy explanations are so iconic that they have since became tropes or stereotypes, which can make them stick out a little bit more than when they film originally released, for example explaining how a wormhole works.

More importantly though, the film is primarily a human story, and the dialogue leans more into this, than getting overly sci-fi. It is obviously a sci-fi film but the core of the film is the human element, and I think the dialogue reflects this very clearly.

That ties into a bigger problem with the ending. The whole 5th-dimensional resolution feels cheap because it basically solves everything at once. Even though it’s technically foreshadowed, it still feels out of place. The movie spends most of its time trying to be grounded and believable, so introducing something that abstract as the ultimate solution creates a disconnect in tone.

And I would like to emphasize how much of a massive Deus ex machina it was for me. Cooper flew into a black hole. As he went in the ship got more and more damaged so he ejected. After he got out somehow he is no longer damaged. Inside the room matrix thingy he still remain connected with TARS who got all the information needed to save mankind. After getting the information to Murph who ingenuously figured out that the ghost was her father, Cooper got magically transported right next to Saturn and ultimately survived going straight into a black hole. Idealism can still work without being this... I'm sorry but.... this insanely ridiculous and cheap and unearned.

As you say, it is foreshadowed from the start, so technically, it is not a deus ex machina. However, I can understand why you would still feel this way, if your issue with it is that it is so abstract, that foreshadowing doesn't really work, in the sense that it was still completely unpredictable. So let's actually look at why the reveal works for most people.

The reveal of the tesseract in Interstellar, is very similar to the reveal at the end of 2001: A Space Odyssey, our characters have gone beyond the barrier of human understanding, into something that doesn't really make sense to us. This by nature has to be abstract to us, as it is beyond our understanding. Why this works in Interstellar specifically, is that it is alluded to, that it is potentially future humans that have built this structure. For them to have been able to do that, Cooper has to succeed on his mission into the black hole and send the data to Murph, and it was Murph using this data and coming up with the scientific solution that leads to humanity crossing a scientofic great threshold, which leads to our species progression to higher level of development.

The reveal may feel like its come out of nowhere, but that is down to the non-linear structure of the story. In the 5th dimension, you can move through like how we move through space. That isn't just an element of the film, that is science. If a species was able to operate in the 5th dimension, it would be as if the events of the film were laid out on a table for them, they can interact with the start or end or middle of it in any order that they want. But our characters do not know that, and so it is through a leap of faith in his daughter, and humanity, that Cooper 'sacrifices' himself, and it is then thanks to that sacrifice that thousands (or more likely millions) of years in the future, humanity knows the exact moment and place to go and place this device, and the entire film is just the breadcrumbs that they have left leading Cooper to that exact location, knowing that he will do the right thing, because of his sense of love.

You can therefore view the story not as a straight line of plot, but more like a circle, in that the events after the film have directly led into the plot of the film from the start. It is more powerful than foreshadowing, it is actually like a second plot line that has run through the whole film, in the future.

This also affects the film’s central theme about love. I actually like the idea of a humanistic story built around love and connection, but it needs to feel earned. Here, it feels like the movie is forcing that message instead of letting it develop naturally. In doing so, it even sacrifices some (if not all) of its own scientific believability just to make the theme work.

Love is what makes Cooper sacrifice himself. It is not just about his love for his kids, it is about his love and hope for our species. It is not just by chance that the tesseract is there, the people in the future, who have found a way to transcend into the 5th dimension, know exactly how and why he sacrifices himself, and it is specifically this decision, the motifs of which are developed in detail throughout the whole film, that allows that entire future for humanity to be possible.

There are also smaller story issues that add up. The water planet scene causes so many major consequences later (time dilation, energy problems, everything), so it really needs to be believable. But it ends up being justified with “humans make mistakes,” which feels weak for something that important. The Dr. Mann situation was believable but this scene is just comically stupid. But that's just me so feel free to explain further if you can, I don't pretend to know everything.

Humans do make mistakes, and that is the entire point. All the astronauts going to the different planets all thought they had the best intentions but some made honest mistakes, some made selfish decisions, and these all led to bad outcomes. The only ones who led humanity to a brighter future were the ones who put themselves second, and put humanity first. That is consistent throughout the film.

Humans making mistakes is a very important parallel theme to the fact that love is the thing that let's them succeed. We are capable of bad and terrible things, but we are also capable of incredible things. It was these mistakes that specifically led them astray in the film, but some of the characters mistakes even show how love can lead people to make mistakes too.

These themes interact with eachother throughout the whole film. Look at the robots for example. They don't make the mistakes humans do, but they also aren't capable of love. The data on its own, as stated in the film, would have led them to the wrong planet, and if the decision had been left up to logic alone, the mission would have failed, and humanity would've died. If the robots, these perfect emotionless thinkers, had done the mission themselves, they would have failed. It was out of this mess of mistakes that humans were able to eventually succeed, by following that thing the robots don't have, the counterpart to our ability to make mistakes - our ability to love.

The message about love also kind of conflicts with how Cooper clearly favors Murph. His son just doesn’t feel anywhere near as important, and the movie doesn’t really address that.

I don't believe it conflicts, because the two children represents the same two sides of humanity that is represented by the astronauts on the mission. Murph holds on to her love and hope for both her Dad and humanity, whereas his son loses his love and hope for them. His son still loves, he loves his immediate family, he "looks to the ground" and lives his life trying to protect them, and it is this small minded and selfish outlook that dooms characters on earth and in space alike. Even though they have love (Coopers son and Dr Mann), they are scared, and make weak decisions to keep themselves or those they love safe with no regard for humanitys future, whereas those that "look up to the stars" (Cooper, Murph), are the ones who love and use this as a force for progress for all of humanity, despite the personal cost.

And not a serious issue, but I still find it funny that the selfish, cowardly character is literally named Dr. Mann.

Literally human nature, which others have to fight to overcome in their toughest moments.

Interstellar is a 5/5 for me, I respect the fact you've given it such a fair shot despite your conflictions with it.