Well well, I was reading one of the four letters a few days ago, the one to Pythocles.
It's intriguing to see someone putting together ideas of how things work with far less information, and in many cases coming to conclusions which are quite right. And others which are wrong.
A sort of illustration of how someone with a sound method understands the world, and what is elayed by the senses. A wonderful read,
A good topic for discussions, for example the part on clouds.
The most striking thing, for me, is how Epicurus presents his various explanations of observations as never the final word, but as a number of different explanations which are all consistent with observation, but different. He makes no claim to give the final word on a topic, but gives a ranges of possibilities.
This ties in with physics in a slightly different sense where science is only ever "the best explanation so far", which will always probably be developed further in time.
Most interesting, that letter. Some thoughts from a newcomer 
