I have two slightly different esp8266-01 modules which i bought from ebay, one has a 8 legged chip that is bigger than the main esp chip and the other has a smaller 8 legged chip about half the size of the other module. The esp with the larger chip gets very hot and the other does not hot at all, so i bought a few more of those and sure enough they run nice and cool too. So in conclusion your esp module is using a cheap component and will get very hot, but will still work as intended albeit a short life maybe.
The hot esp chip, note my one was black not blue but the same pcb components.
