This was a Charlie centric episode. I thought that it was very moving. It shows Charlie's struggle with withdrawl from his heroin. It shows that one can be strong enough to overcome his weaknesses. I think that Locke made really good comparisons with the boar and the moth. And we can all pretty much say that Charlie is "the moth".
This episode also shows a somewhat good bond between Charlie and Locke. Though Charlie was mad with Locke for most of the episode, in the end Charlie knew what Locke was actually helping him rather than torturing. I also like how Charlie, being the "useless" one, rescues the "hero" Jack in the cave-in.