Funny, I just rewatched episode 18 again, this time in dub. Now now, before people start raging and flaming at me for doing so, I felt intrigued to do it. Besides, Netflix had it up there, so why not?
I can't say the dub was awful, because its definitely a step up from other dubs I've seen in the past. On the other hand, the dub wasn't great either, especially when it came to pronuciation and localization of certain names and parts (first and second respectfully). The spoiler'd moment that was mentioned by Malakai0, was actually halfway decent. I still got the sense of emotion and the voices didn't throw me off from the scene. I will say though, half of the reason probably came from the fact of how many times I've seen it in Japanese, that I still think of the Japanese version regardless.
The best scene in Clannad, in my opinion.