In solo queue, she's one of the most hated champions because she does disgusting amounts of damage with some of the best mobility in the game while being completely resourceless. This is why she sees bans quite often.
However, Riven is almost never played competitively, and teams almost never use her.
My question is, why? What is it about Riven that makes her scary in solo queue, but worthless in competitive play?
ScurvyNave3 votesI believe that in solo que or normals you have less control over who your team picks to counter Riven. Its easy enough to counter pick her or simply bank top and shut her down early when playing with a competitive team.
In solo que as a top lamer you are generally on your own unless your junglier is wise enough to lend you aid at the right time. Riven's massive early damage pluss her lack of mana means she can out push and out trade most tops at early levels with only having a 
for sustain.
However, competitively Riven is a cc vulnerable fighter who falls off late game and needs to be tanky but also deal damage to be useful in team fights which is what competitive is mostly about IMO. In solo que she can out-duel many champs but when she gets snared by a lux or morgana in a team fight there goes most of her up front damage.
In general Riven is like Katarina in which they are nigh-unbeatable in solo que but a communicating team can easily destroy.
AetherKingdom1 votesIn general Riven is like Katarina in which they are nigh-unbeatable in solo que but a communicating team can easily get destroyed because both of them are stupid in design. ftfy
Drunk Rummate1 votesI don't think anybody builds dorans shield on riven. She has a shield that scales with AD to serve as defense, and the sustain from DS isn't very good. Most people pick Longsword + 3 pots if they have a tough lane to sustain through (like Jayce), and dorans blade if they have an easier lane (like Nasus) and they can afford to sit in the minion wave and sustain through autos.
ScurvyNave1 votesI just put in Doran's shield since thats what I see people buy first when I play against her.
Marmara1 votesI agree with the "massive early damage" part.
When facing against fighters, most champions can easily get by without building armor. But not Riven. You HAVE to build armor when facing against her. It's mandatory.
Yeah I know... very infuriating. But at least she only deals physical damage. It's like counterbuilding Leblanc with a negatron cloak.
Genocide Victim1 votesRiven is the perfect pubstomper, just like Akali. Snowballing out of control almost never happens in competitive play so Riven and Akali are both quite bad.