This was originally supposed to be aired as episode 10 in the DearS TV series, but wasn't aired mostly due to excessive nudity. (It's Barbie doll nudity) It was released with the DVDs as an extra episode and is sometimes labelled as episode 13.
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.
I've noticed that there are 3 types of Anime specials.
The first type is the "sequel" type - it basically wraps up any remaining loose ends in a story (this is used when there's not enough loose ends to justify making a second season, but the ending doesn't tie up all of the loose ends).
The second type is the "side-story" type - these can either expand on a scenario that is briefly mentioned in the main series, or they can just be a scenario that could have happened, but when is never really specified (if it's the latter case, there's generally a fair amount of fanservice
in the special).
The third type is the "unaired" type - Basically, they take an episode that they originally had as part of the main story, but were unable to air due to content in the episode.
The DearS special falls into the third type, but also kind of fits the second one.
Story - 4/10
It's a basic hot springs episode - and there's a lot of nudity. You can tell that it was meant to air as part of the main TV series, since it seems like they try and advance the story when they aren't focusing on the fanservice (at least, that was what I got, since the site I watched this on had this special listed as episode 10, and the ending listed as the special for some odd reason). However, the fanservice is pretty excessive - so if you don't like a lot of fanservice, you should probably stay away from this special (although you probably shouldn't watch this special in the first place if you haven't watched the TV show it's attached to).
Animation - 4/10
The art is the same as the series. It kind of reminds me of the animation style from Gundam SEED, except it's not nearly as good. The art is colorful, but the style they use isn't visually appealing.
Sound - 5/10
The soundtrack is just forgettable. I couldn't really name anything notable. I don't rememberr the voice acting being particularly good or particularly bad.
Character - 5/10
My opinion on the characters for this show is a case-by-case basis - while I actually kind of like Neneko, there's also Mitsuka, who just irritates me (she's like what would happen if Yurika Misumaru or Misato Katsuragi was much more sexual, and didn't have any of the other traits that made her likable). Overall, however, my opinion on the cast is just "meh".
Enjoyment - 3/10
The only reason I watched this was because of how bad I had heard the main series was, and the site I watched it on had this listed as episode 10 (and the last episode was listed as the special). It's a good timekiller, but that's it.
Overall - 4/10
You probably shouldn't even watch this if you haven't watched the main series, and the special isn't really worth sitting through the entire 12 episodes of the main series. Just go watch Heaven's Lost Property, Ai Yori Aoshi or Chobits if you want something similar to this that's much better.
Alternative recommendations (for both the Special and the entire series): Chobits, Heaven's Lost Property, Ai Yori Aoshi, Oh! My Goddess