Is Buddhism monotheistic?

Buddhism is monotheistic in the sense that all is god and god is all. Although there are many different Buddha figures, they all represent the same Buddha.

Answer

Yes, it's monotheistic in a pantheistic sense.

No, it is not monotheistic if, by that, is meant one transcendent supreme creator God.

Answer:

There is no personal "god" in Buddhism. The concept of a supreme being does not exist. Buddhists feel they achieve nirvana, a cessation of the cycle of birth and death (reincarnation), essentially a state of no-mind by their own efforts.

The Buddha figures are not idols or gods.