I might pretty much give the general details of some of the creatures powers - usually the at wills and powers that might define it such as a dragons breath weapon and fear or the fact that some creatures change when bloodied. Generally things that seem racial.
I don't give information on powers that I rate to be unique to that creature such as the various powers of an eladrin arcane archer or orc chieftan. The main reason is in my compaign many creatures are unique and I swap powers around. If someone was to see what looked like an orc chieftan there would be no way of knowing what powers he had until after he had used them
The rules are open enough to allow you to fully explain all powers or just give basic info about one power. I play it by ear