There is not one generally accepted definition of what religion exactly is. But a lot of Buddhists seem resistant to calling their faith a religion. They like to believe that their faith is fundamentally different from other (theistic) religions, because it is based on the mystical experience, which is supposed to be beyond the mind and therefore beyond conventional religious belief. Yet Buddhism is actually very much a religion.
Religions are characterized by laying claim to having the definitive answers to the great questions of life, such as who we fundamentally are, the existence or non–existence of God and what happens to us after we die. Buddhism, like all other religions, also claims to have the unique right answers to these questions.
Additionally, just like other religions, Buddhism portrays life as a kind of learning school, in which we have to undergo moral trials. Passing or failing these trials determines whether we subsequently will get into a better, more heavenly realm or a more hellish realm.
Also, all forms of religion depict human beings as if the universe revolves around them. In Buddhism, this universe is also seen as a stage for our spiritual quest and the human realm is regarded as the most favorable realm to reach salvation.
So clearly, Buddhism has all the hallmarks of a conventional religion. Buddhism arises from the same human yearning that lies at the basis of all religions. This is the human need for finding a reason for our existence; some religious story to makes sense of it all.
I may think that Buddhism comes up with a more intelligent story than other religions, but that doesn’t change the fact that Buddhism exists in response to our basic religious need in much the same way as other religions.
This religious need is a natural outcome of human intelligence. It arises from people’s ability to ask deep questions about life. But as far as religions go, the questions are often more interesting than the answers, because the questions are universal and real, but the answers are exclusive and debatable.