Rambam's Characterization
Rambam refers repeatedly to the Mutakallimūn (Kalam philosophers) in his Guide to the Perplexed. Some examples of his characterization of Kalamic thought can be found at the end of Book I (Chapters 73–76), see also Wolfson (1967). The translation which follows is from Pines (1963):
As for that scanty bit of argument (kalam) regarding the notion of the unity of God and regarding what depends on this notion, which you will find in the writings of some Gaonim and in those of the Qaraites, the subject matter of this argument was taken over by them from the Mutakallimūn of Islam and that this bit is very scanty indeed if compared to what Islam has compiled on this subject. Also it has so happened that Islam first began to take this road owing to a certain sect, namely, the Mutazila, from whom our co-religionists took over certain things walking upon the road the Mutazila had taken. After a certain time another sect arose in Islam, namely, the Ashariyya, among whom other opinions arose. You will not find any of these latter opinions among our co-religionists. This was not because they preferred the first opinion to the second, but because it so happened that they had taken over and adopted the first opinion and considered it a matter proven by demonstration
— Rambam
Rambam continues in that section to provide a history of Kalamic thought, its sources and subsequent development, and then proceeds to condemn a certain laxity of thought to be found in this philosophical school. In particular, Rambam takes strong issue with the Kalamic proof of God's existence and unity from the Creation of the World in time. While Rambam himself does regard the world as having been created ex nihilo (rather than being eternally existing, as Aristotle would have it; see GP, Book II Chapter 25, for example), Rambam also considers this proposition as being far from obvious, and in all likelihood not susceptible to proof. He thus regards the Kalamic approach as starting from a position of convenience rather than from an irrefutable premise, and their methodology as being entirely tainted by their eagerness to produce certain results which support their prior beliefs.
Additionally he considers their premises to "run counter to the nature of existence that is perceived." He writes that "every one of their premises, with few exceptions, is contradicted by what is perceived of the nature of that which exists, so that doubts come up with regard to them." However, it can be noted below, that in many cases the Kalamists were indeed more prescient than Rambam himself in their beliefs regarding the discrete nature of matter, existence of vacuum, and other physical characteristics of the natural world.
Read more about this topic: Jewish Kalam