If you go in expecting a director to have made the exact same choices you'd have made, it just won't work. However, that seems to be what some people expect. They think this director who has never met them and did things as he/she saw fit should have done this or that, just because the viewer wants it. Then the viewer gets unhappy, sometimes even mad because the movie didn't follow the script in their head. Those are unrealistic expectations, in my opinion.
You're absolutely dead on with this. One of my biggest pet peeves is when people want a movie to go their way and then lambast it for going a different way. I think it's much more fun to see how a filmmaker interprets material rather than strictly adhering to it. For example, I love comparing Burton's Batman, to Nolan's Batman, to Snyder's Batman, or Raimi's Spider-Man, to Webb's Spider-Man, to Marvel's Spider-Man, etc. It's fascinating to see what specific aspects of a character or material are considered most important to a director, as it's a window into an individual's worldview. I love it.
With Suicide Squad, I've seen the trailers and I personally don't get the hype. It just doesn't look good to me. Though, sometimes, I will watch a trailer and not be impressed, only to wind up enjoying the film. Other times, it's the opposite. And, of course, trailers can be dead on sometimes as far as how I will or won't enjoy a film. But, I'll see it, likely when it's on streaming or disc. I don't need to go to a theater to see it.
Trailers are tricky. I once visited E-Film (one of the top color correction facilities in the world that also cuts together about 90% of the trailers you see in theaters) and they told me that they rarely see the directors working on trailers. It's most often the marketing team, whose goal is to just get your butt in a seat rather than give you an accurate representation of the movie. Occasionally a director will give input on trailers (like James Gunn for GUARDIANS OF THE GALAXY), but it's very rare, as they're usually ridiculously busy working on the film itself.
All of this is to say that I think trailers should be thought of as their own separate work from the film. You can enjoy them and let them hype you up, but always remember that the movie itself could be completely different because different creative voices are working on it.
Personally, when it comes to film expectations, I do expect a lot, but the only reason I do that is because I want to love a movie. I don't go into any movie wanting to hate it, I just want something good. I just can't bring myself to enjoy sitting in front of a screen for two hours numbly consuming something; I need to have it cause some kind of reaction in me.
Now, even with my high expectations, I am pretty lenient. If a film is terrible but has one masterful performance from an actor I will recommend it for that reason, or if the plot is stupid but the action scenes are impeccable I will likewise recommend it for those. A good example of this is FURIOUS 7, which is a very dumb movie, but the car chase on the mountain is straight up one of the best action sequences of last year and should be studied in film schools, plus the sendoff for Brian at the end is gloriously sentimental. Those two things alone make me love that movie and, as a result, make it worth recommending.
While I do expect a lot, I also understand that filmmaking is incredibly complicated, so as long as a movie does one thing really well I recommend it. However, I do like it when something great comes along, so I search for those movies every year and, whenever I find one, I talk about it until people get sick of me.
That's my approach to movie watching in a nutshell. I'll never not watch something, and I always enjoy going to the theater so much that even if something is terrible I could have fun (at home I'm a bit grumpier), but I do hope to find some form of greatness in everything I see.
