Reiki is essentially whatever you make it out to be. It is merely a system/method of channelling/directing the Life-Force energy - the KI in Reiki, if you will, also called Chi; Prana, etc.
If you believe in the power of Reiki, and use it often, you will indeed feel its awesome power.
I received my Reiki Master training/attunement over 10 years ago, and since then I've been awed and inspired by it's tremendous power.
And yet at other times when I've placed it on the back burner, I've at times forgotten its power and occassionally even doubted whether it worked at all, or was my mind just playing tricks on me. Weird.... huh...
So basically the more you use it, the stronger it gets, just like a muscle.
May have something to do with my intent at the time, which was primarily for the healing of Gaia - Mother Earth.