another please rework pyke-thread but this cannot be stated enough until it's done.
first off the most obvious one - his ult. the fact that it executes (negates 100% of your armor if low hp enough) instead of just dealing damage, it scales with your AD and it has ridiculous range, meaning that you can ult the whole enemy team even if they are scattered far away from each other - in a line retreating to base or all around the jungle - doesn't matter because the range is so long. and the fact that it resets every time it kills someone. darius has this same but with much shorter range and with zero mobility, so it requires very specific situation for him to be able to execute even two players in a row. and in difference to darius, pyke's R also acts as a teleport. could literally split it in two and still have a perfectly decent ult.
second, his Q has next to no cooldown at max rank and full build. thresh with the almost identical Q has twice as long CD, with the exception that it will always hook you on the opponent, preventing you from using AA at the time. pyke can just enhance his dmg in a close combat with the Q without losing any precious time of his.
if this didn't already make him broken enough, let's give him a dash with short stun ability to cancel some cool stuff like MF or Kata ult, and some nice extra damage. again also with next to no CD at max rank. but most importantly, a nice mobility boost to further enhance his ability to kill everyone with his ult.
and finally, a freaking invisibility ability with sick mobility boost and heal, and with such low detection range that you can execute low hp players without them ever knowing before it's too late.
to summarize it, his every ability has perfect synergy with his ult, and the ult itself is beyond broken with no real ways to counter it, other than not losing any hp in a fight. if you'd remove thresh Q or R, darius R, singed R, urgot R, bliz Q or basically R from any champion you'd be left with the worst champion in the game, but remove Q or R from Pyke and you'd still have a totally decent assassin with great support capabilities. without his Q he would still be probably the top 1 assassin in the game, but at least we wouldn't see him as a support executing the whole team at once. Remove his R's reset feature and replace it with a on second cast-dash or just teleport for example, and he'd be totally fine already.
I don't know enough mathematics to calculate a ability value to a champion, but without a doubt Pyke is worth 2 any other champions at his current kit. on the other hand i must say that Pyke is insanely rewarding to play because the kit is so unique and has so perfect synergy, and because he's difficult to play well with high skill cap - it's not that you'd have to rework him completely - the numbers just need to be nerfed drastically to make him worth a normal champion. right now he's worth too much even on average hands, and with the high skill cap comes even more impact on the game if you know how to play him right.