Yotsunoha is a two-part OVA that takes its cue from a hentai game for the PC, which should give you a pretty good idea about most of its major plot points without saying anything. High school, one guy, several girls with wildly varying personalities and physical characteristics, etc etc.
To be more precise, this show follows three girls (Nono Nekomiya, Iori Yuzuki and Matsuri Amachi) and one guy, Makoto Yuki, who we first see on the last day of their current school before it closes for good. The group buries a time capsule and agrees to meet again to reveal its contents three years later. We then fast forward to exactly that time, giving this episode plenty of excuses for flashbacks and reminiscences while also dealing with the current feelings and thoughts of the group.
Beyond the slightly intriguing principle of the time capsule and meeting three years later, what follows is pretty much anime cliché, with at least two of the girls harbouring feelings for Makoto, who of course is more or less completely clueless of this. It isn't bad per se as an OVA goes (although Nono's drawling voice really annoys me for some reason), and the main characters are all somewhat likeable in their own predictable fashions, but it doesn't look likely to break with convention or bring anything new to the table, instead offering some reasonably easy-going entertainment. If you like this kind of thing a lot (or maybe if you played the original game), then Yotsunoha will probably work pretty well for you, but otherwise there are plenty of better examples of this genre around judging by the first half of this OVA.