This is pretty much your standard fanservice episode - there's not really character development or plot, the episode is here for the fanservice. That said, despite the fact that I generally don't like fanservice episodes, this one didn't go so far as to totally distort the characters or tone of the series, so I didn't dislike it. Given the style of show DearS is to begin with, a fanservice episode doesn't go all that far away from the tone the series already had.
So, if you enjoy your guilty pleasures, you'll probably like this episode, if you're not really into it, it's probably still worth if you liked DearS. If you haven't watched DearS yet, but plan to, you could watch this where episode 10 should happen, since that's actually where it's supposed to be. Overall, it doesn't really matter much since it doesn't really affect the story.
