Please refer to the website http://www.sanatansociety.org/hindu_gods_and_goddesses/shiva.htm
where Shiva, Vishnu, and Brahma are all mentioned as separate gods.
I am not by any means an expert on Hinduism, but Shiva is mentioned as having different faces, but not as being encarnations of the other two Gods mentioned here, and Vishnu, I believe has 8 incarnations. There also a Kali, goddess of time and death, among others.
There is one underlying reality that is Brahman. One reality that is God and God alone.