My name is ryoh on the NA server. I am a Platinum (if I win promos, Plat 1) Kha Zix main with over 100 games played as Kha Zix. Kha Zix is an exceptionally strong champion because of his mobility, huge burst damage, sustain, and invisibility.
Kha Zix, while being nerfed many times, is still a very strong pick in S4. Back in S3, Kha Zix was a very popular champion because of his W, which was pretty broken. Riot wanted him to be an assassin, which the W meta wasn't doing, and switched power to the Q. Plus, since there were oracles and plenty of wards, it was easy to counter his ultimate and passive. But now in S4, since there is a limit on wards and there are very little invisibility counters, this was an indirect buff to Kha Zix and all champs with invisibility.
I know, the Win Lose Ratio SUCKS. I played a lot of top Kha Zix when I didn't know how to play him in the beginning of S3, I think I went like 3/12 back then. So considering that, it's not all THAT bad.