I liked it a lot. It was clearly a cheaper filler episode, so I took it for what it was, but was pleasantly surprised.
It reminded me a bit of 11:59 from VOY, which I hated. But I liked Carbon Creek because of the culture shock aspect that always makes these types of things fun, such as Carpenter St, TVH, Year Of Hell etc. The fact it wasn't technically one of the cast didn't bother me as much as it did in 11:59. I thought the story was nice, and the characters worked well.
How a Vulcan managed to survive his life without being detected through any illness, accidental ear slips, Pon Farr sex-rage etc is beyond me.
One of the surprisingly good episodes of S2 for me.