Kyoukai no Kanata was aired in 2013, and with its 12 episodes it is one of the rare animes not based on ongoing manga with no end in sight. You can read the details here.
If you decide not to watch KnK you will not miss out on an anime that would plague you and beckon you to rewatch it every once in a while. You will, however, miss out on good animation, approximately 240 minutes of good fight scenes, fun and fanservice.
Any chance at greatness KnK might have had was defeated with the story which is reminiscent of a whole myriad od anime series, not excluding the ever so popular Bleach. Instead of Hollows, you have Youmu and they are not hunted by Shinigami but by Spirit World Warriors. A smidge of originality resides in the way main female character, Kuriyama Mirai fights (her blood). This, however perfectly animated, has not been utilized sufficiently to compensate for the overall feeling of deja vu.
The characters, their quirks (Little Sister Complex, Megane Complex) are fun and easy to relate to (weird fetishes excluded). I literally shed a few tears laughing during episode 6. KnK is finished, very finished which gives it a sense of closure I find lacking in most new anime series. Sure, if they felt like it I’m sure 200 episodes with idiotic fillers could be made.
In conclusion, if you want to watch an anime which will divert you, make you laugh and care about the characters, you should watch Kyoukai no Kanata. If you want originality, something that will make you wonder about people and the world, something that will make you sit on the edge of your seat, try something else, one of these maybe.
I do, however, recommend watching episode 6, for the pure fun of it.