It was adapted from an adult visual novel, which explains a lot. It's innocent and tends towards "pointless", yet no clear reason is full of bath scenes and panty shots. (Nonetheless, the art's too childish and of-its-era to be sexy and you'll probably stop noticing the fanservice. When Ai has sex, this is handled so discreetly that I didn't realise and only found out later by googling.) The fanservice is weirdest with Shizuku, who appears towards the end and occasionally has her tits out for no reason while standing in a field.
In the day, it got an English-language DVD release from Sentai Filmworks. These days, the show's become persona non grata due to age issues. Ai is 18 years old, Mai is 14 (at first) and Mii is a young-looking 11, so you'll see fans scrubbing references to the show from the internet.
GAME = has a male protagonist (Chris) who can have sex with any of the female characters. Yes, including Mii. Ewwww. He starts living with the three sisters and their android maid in a time-travelling house. The game repeatedly made the top 50 list of bestselling bishoujo games in Japan and spawned an Internet meme called "Caramelldansen".
ANIME = there's no Chris and the show feels almost kiddie-oriented. The main cast is all-female. They're still living in that time-travelling house but now going on a quest, semi-guided by Ai. She talks to flowers. They're looking for Shizuku. The show could be said to be about farewells and separations, since the girls have no control over their journeys and have almost no time to make friends anywhere before they disappear again. That's particularly hard on Mai.
This show's biggest problem isn't its fanservice, I'm afraid. Its cast is lacklustre and I don't find its central idea convincing.
The only successful main character is Mai the tomboy. She has issues with the time-jumping thing and she has a genuinely tough time in two episodes. Of the others, though, Ai is easy-going and has big boobs, but displays very little mental activity. Mii is loud, childish and uninteresting. (She also loves talking about breast size.) The lazy, unfriendly android maid is actually a workable character, but hardly ever gets involved in episodes. The pet ferret who can theoretically turn into a human never does so and I often fast-forwarded through her post-credits sequences.
Then there's the show's core concept. The girls don't want to tell anyone about their time-travelling house and we're supposed to see their predicament as almost tragic. I don't get it. What's so difficult about telling people that you're travellers and that you'll only be here for a few days? To me, their repeated communication failures were a flag saying "idiots". (Also, why didn't Mai even try to visit Konami in ep.9?)
In fairness, there are above-average episodes. I liked Mii cheering up a girl in hospital in ep.3. The deserted villages and the android maid are quite good in ep.4. I was wondering if we'd been talking to a ghost. I liked the episodes that loop back to previous ones after 30 or 40 years. Basically, though, these are detours in the show's uninteresting journey from "dull" to "badly thought through". And that's in addition to the yikes factor of underage fanservice.