A supreme being, a creator, is by definition unknowable and indefinable. Thus, I've always been deeply suspicious of people who claim to know God and what his rules for mankind are. Usually, these rules an views are those of the person speaking. For example, people with right-wing political views believe in a God who has right-wing views and people with left-wing views believe in a God who has left-wing views. In other words, God is used to support the individual's own beliefs.
Personally, I feel that the purpose of our spiritual lives is growth and development. Buying into one of these "off-the-shelf" Gods prevents any of this growth at all. God in this sense comes complete with a set of ready-made traits which just so happen to dovetail exactly with the church leader/preacher/priest etc.
I feel that one needs to find one's own way in one's spiritual development. However, I am not anti-established religion. For some people, this may indeed be the best way forward and, if so, then good for them. what I do object to is mainstream religion's attempts to foist their beliefs on everyone else. People are responsible for their own religious/spiritual development, not that of others and I certainly do not need other people attempting to force their spiritual/moral/political/societal beliefs and opinions on to me.