I think it depends.

When my sister saw it, it was very early on, prior to any pub or wide release, at a festival (or something) were it was presented as basically a true found film/documentary. She called me almost immediately after seeing it and pestered me for months to go watch it, presenting it as truly great.

When I saw it, I knew it was fake, had read about the making of it, etc. We were laughing at it in the theater (especially the "found my cigarettes" part). So, while a little scary in parts (especially that ending), it wasn't anything special to us. We still point to Event Horizon as our favorite horror movie, partly because we didn't know it was going to be what it was. We thought it was more of a space exploration thriller.