So far, you're in production order. The Wikipedia entry has them listed in airdate order on the main chart, but also has a smaller production order list: http://en.wikipedia.org/wiki/List_of_Star_Trek:_The_Original_Series_episodes#Production_order
"The Enemy Within" is a personal favorite of mine. Half the plot is based on a continuity oversight that nobody will ever be able to explain to satisfaction in-universe (they didn't use the shuttlecraft because they hadn't been established onscreen yet), but it's such a great story anyway--The basic concept of Kirk as a split being with neither half being the whole Kirk is great; Shatner gives us a hammy tour de force; and we get the births of the classic "Big Three" dynamic and the Vulcan neck pinch.
If you're enjoying so far, you're in for some good stuff in the very near future--production episodes 7 and 9 are routinely put in Top 10 lists.
Well I'm certainly appreciating them.
In the past, I've watched TOS Movies a few times, but they for the most part seemed a bit lacking in some areas.... mostly I think is because the actors were older, thus less of the action judo chop fights you see in TOS. Then I saw the reboot movies and they're nothing but action action action.
Nothing wrong with that, I love the reboots.
But it does seem to all fit in.... as they were younger, they took bolder steps and actions. As they got older, they relied more on experience.
Similar to the Picard Complex.
Many consider Picard less of an action person and more of a thinker.... but this is the same guy who got in a bar fight with three Nausicaans and stabbed in the heart for his troubles when he was still in the Academy, who killed multiple terrorists on his ship (single-handedly) like a SpecOps guy.... and has gone through a lot of crap during the TNG series.... and movies.
As he got older, he wasn't all action.... but could pull that card when he needed to (Fighting Klingon Assassins while trying to help Worf clear his name)
Same with Kirk. We see him in the Reboots as going more action than thinking (Younger).... in TOS he's kind of in between, and in TOS Movies, he's older and goes more for wit.... while still tossing in a punch here and there.
As for the Enemy Within, you get the first Vulcan Neck Pinch, and the first reference to "Phasers Set to Stun"
It's all pretty interesting.