It can vary. Depending on your level of lucidity etc, it can be blurry and fuzzy and not at all that realistic. (This can usually be cleared up however with a commands such as, "Clarity NOW!") But it can also be extremely realistic like real life. As Toledous stated, it can seem even MORE real than real life, almost like your senses are enhanced or something. It can be quite the extreme experiance, but as stated it varies.