I really liked how it told the story of someone going through so much hardships, mental illness, drug addiction, being with someone who nurtures your bad habits, and the likes in a "hallucinogenic", sci-fi-ish kind of way.
It felt like it was done in the point of view of the main character, Greg. If it was you or me who's under such heavy depression and drugged like he was, we would probably be in a similar state of mind, escaping into our beautiful, happy place and such.
Even us as the viewers won't be always 100% sure what's real and what's not.
I think the only downside of the film is people not taking Owen Wilson seriously. Which we should. He's not the best actor but I appreciate that he's trying genres like this.