Personally, I tend to give the benefit of the doubt to creators by default because filmmaking is such an intricate medium that allows for such a wide range of ideas that you really can't rule much out broadly speaking.

For the most part, don't worry too much about whether something is 'pretentious' or not, dig into it if you find it worth digging into.

One way of going about it that I think is pretty standard and solid is to just start deconstructing scenes and seeing how they hold up at a macro level. There are a lot of decisions that go into making any given scene and more often than not things aren't left to chance. So your task is to 'reverse engineer' the decision making process in a sense and try and piece together why something was assembled the way it was as well as how it might relate to other moments, what functions for what and how it all connects to any ongoing ideas/themes/concepts.

From there, you can also look at the filmmakers themselves. Often you'll find repeated ideas being approached throughout their work, where you then start to look at how they go about doing that and the ways in which they evolve. Either way, you start to get a more filled in picture that tells you more about what to expect.

The rub, though, is that sometimes a movie can be 'bad' even when it is intelligently put together and contains depth and is thoughtful and basically does everything 'right' structurally. In that sense, I think it's fair to say it fails as a movie but it can still be interesting (and rewarding!) to break it down just the same.

That's also where it gets more subjective though, I think. Because failing 'as a movie' basically just means it couldn't connect with you(or the audience, or everyone) emotionally. That's that alchemy of moviemaking in how once we're 'in', that can be enough but if something breaks the immersion, it can be tough to win back.

Of course, that's all assuming fairly standard movie stuff I think. When you get into surrealism outright, sometimes the goal is expressly to try and dodge analysis and avoid structure for no other reason than a contrarian sort of 'just to do it' impulse. Like trying to write a book without sentences, there might not be any reason to do that but the doing of it might still make you think/feel something, in which case, just dwell on that a bit and go from there.