So yes, I began watching this for KSH but 2 hours of this director's navel-gazing was hilariously gruelling.

Some of my observations:
• Visually, it was gratuitous and self-serving. There were clear allusions to "deep" metaphors, but none of them were actually related to the plot or pushed it forward. They were just there because navel-gazing.
• Plot-wise, the director was quoted (and very obviously hinting throughout the movie) that reality is subjective, yet the movie retains its temporal quality and follows a chronological format instead of questioning time and space with narrative techniques, it just throws a lot of visuals at you in hopes that METAPHOR!
• Perception is not the same as reality. There are arguments that perception alters reality, but for the most part, the physical world follows a universal truth. If this story WAS entirely in his head, it would be a much more riveting movie than what it turned out to be. How can you challenge reality and exist simultaneously in the physical plane? This movie does not challenge anything. It tried to be art but ended up as a lot of visual polish on narrative turd.
• The acting is pretty good but that's hardly the problem here
• The story itself is not complex. It's extremely simple but made convoluted because INCEPTION!
• Just to be clear, I understood the story - but I did not like it. I thought it was extremely poorly executed and the point it was trying to make contradicted itself in how they actually made it.

EDIT// If you'd like to see a well-executed storyline that uses drug abuse/addiction to alter perception/reality, I suggest the Ep2, Season 4 of Sherlock (with Cumberbatch) and see how well they handle that subject.