i'd suggest you try out Wukong. i think this champ is very similiar to riven in terms of snowballing (out of control) when ahead. that said wukong is a much safer choice then riven for just simple reasons:
i find wukong to be one of the best top lane carry champs in soloQ. he has a 53.6% winrate atm. it doesn't say anything but i find people REALLY underastimating the potential this champion has especially when played in top lane. his build paths are very flexible just because so many items fit him well. the best build path right now for him is the assassin build just because the items are so strong right now. core build is very similiar to riven's which is: ghostblade > BC > Hydra. after that you want to build swifties in most cases. last two items will depend on what the enemy team has in power. Maw, steraks, deadmans, Visage, randuins and even GA are all viable items on him. most of the time you'll see me build maw and deadmans as last two just because they compliment his kit very well.
as wu (even when behind) you'll never be useless because of the teamfight potential he brings. the only downside when behind is, that you will do less damage then you would do when even/ahead. the reason for his great teamfight potential is his ult. which provides an AOE damage knockup. this ult combined with his core items can pretty much 100-0 any squishy and can shred tanks for your team thanks to the passive of BC which combined with his ult applies max. stacks in less then 2 seconds.
all for all i think wu is a really fun champion to pick up and is a champion that won't bore you very quick (W abililty is so fun xD)
if you have any other questions about wu just hit me up as he is my main (200K mastery level 7) :D