This place really does need more stuff to post on.
Higurashi's a horror-mystery anime about, basically, people going insane and usually ending up killing most/some of the other main characters. Every 4-6 episodes is another 'arc', the story starting over a while back and playing differently. There's three seasons, 26 episodes in the first, 26ish in the second and 4-5 in the third.
The first season is mainly getting to know the main characters, piecing together more fragments of the story every arc, and watching the one character go insane every arc and have the others die. It's pretty gory. Most of the time, the first episode will be your average 'cute, lolis and peplez doing st00f', the second is usually more serious, more story, and the start of someone going insane and killing people. The third is usually the same, but by then you should know pretty well who's crazy, so you'll be waiting to see what happens. The fourth and sometimes fifth episode is usually the gory murder/torcher/most important story pieces. The first three are just set up for it basically.
Keep in mind the mystery is
not "Who killed who". It's figuring out the backstory, and then why they're going insane in the first place.
Behind the murdering/death though, the story really is interesting. If you no-life your computer often, you'll probably get addicted like so many others and watch 8 hours of it in a few days. If not you'll come back here and tell me how stupid it is, how stupid I am and how stupid life is. Whatever.
The second season is about Rika, how she's been reliving the story through all the 'arcs' for technically around a hundred years. She's the only one that remembers the past each time, usually. Towards the end of season 1 and in season 2, some of the other main characters start remembering things, mostly that they went insane and killed people. They tend to keep eachother from killing people in this season more.
Basically, watch the first season for sure. If you're at all interested in the story, watch season 2. If you just want gore, I hear you should check out Elfen Lied. There's always comments saying "Eh, that's okay, but Elfen Lied is way worse."
Season two; Mion, Shion, Rena and Keiichi beating the crap out of some noobs who wanted to kill Rika and Satoko. Season 1 on anime-sub.com. I'm sure Elfen Lied is somewhere on anime-sub too, but I can't be bothered to find it.
*ALSO*There is actually a third season, about 5 episodes long, "Higurashi no Naku Koro ni Rei", replace Kai with Rei. The first episode's... 'Your average anime', pretty funny I guess. The second.. Crap happens and you'll wish it didn't. ^^ Then two episodes and the 'end'. It turns out fine, but Hanyuu is a little bit of a jerk. >_<