If you go at it with the attitude that this is simply a reason to get high, or to observe visual disturbances for the sheer sake of hallucinating, there's a very good chance that will comprise your experience. Conversely, if you set an intention of learning about yourself, life, death, existence, the universe, etc., and approach it with regard, then there is a very good chance you will have that experience.
From what I have gathered observing myself and my friends, the latter can be quite transformative to the self. It can encourage profound positive changes in attitude and improve quality of life, increase spiritual awareness and feelings of interconnectedness, greatly diminish or eliminate one's fear of death, among other things. These feelings can last, sometimes for life, and it can take months to fully integrate the lessons learned and information gained after returning from the "journey". See the John's Hopkins study on psilocybin for more information.
Preparation and intent simply cannot be understated when it comes to the use of these substances. What the psychedelic enthusiasts refer to as 'set and setting'.