This isn't Yuru Yuri Season 3. It's an hour-long OVA and a couple of one-off TV episode sequels that were released as part of the run-up to Yuru Yuri San Hai!, i.e. Season 3. Normally I might have been reviewing the OVA separately, since it got a theatrical release and so is technically a stand-alone movie, but here it hardly seems worth it. It's Yuru Yuri. It's always the same. Schoolgirls do schoolgirl things. They're all lesbians and some of them fancy each other, but that never goes anywhere and the show's just good-natured light comedy.
The OVA has better art than usual. The character designs are unchanged, as is right and proper, but the backgrounds are more finely drawn. (This might be just due to the show being made by a different studio, though.) It also starts with a silly bit for laughs where the show pretends to be a English-speaking hard-bitten macho action series.
The plot is mostly about camping. The girls will go camping, although before that we've got lots of silly conversations to catch up on! We briefly meet everyone's various sisters, while Kyouko made me laugh. "What kind of perversion is this? Include me!"
Sakurako has orange hair! When did that happen? Was it always like that and I never noticed? I presume that's so we don't confuse her with Kyouko, although if so then I'm puzzled about Himawari's vanishing pigtails. (UPDATE: no, I'm wrong on the latter. Sometimes she has them and sometimes she doesn't. Presumably she likes changing her hairstyle from time to time.)
...and that's it. That's all I have to say about it. It's that kind of series. You watch it and it's amusing, but it's liable to seem all the same even when it isn't. This OVA's keywords are "relaxing" and "nice". Camping stuff happens.
After that, unusually, the two TV episodes are both sequels to the OVA, referring back to its camping trip and especially to some photos that were taken. (Nothing indecent, though. They're simply undignified. Kyouko photographed everyone while they were asleep. She's like that.) There's also a bit where Himawari says nice things about Sakurako and... wait, was that it? That's the end? Oh, okay. Seriously, though, even slice-of-life shows generally find more conclusive endings than that. However it hardly matters, especially since when this was broadcast, Season 3 was starting inside a month anyway.
That's all I have to say. Yuru Yuri defies analysis. It just is. I quite enjoy it, but I probably wouldn't notice if you took it away. Nachuyachumi is the Japanese word for "summer holiday", incidentally, but pronounced in a way that suggests you're talking to a three-year-old. Next up: Season 3.