What are Riven weakness?

Incredibly ass health regen that makes her outright lose to any sort of harassment champion in lane after level 2.

Extremely difficult to play PROPERLY-there's a world of difference between Rivens who can animation cancel and Rivens who can't.

short range.

squishy without her 2 sec sheild

Riven is effectively a liability to her own team when behind. There's really no safety net or fallback plans, she either wins lane and carries from there or fails miserably.

Every other top laner can build tanky, brings some innate utility or can do something useful with limited gold. Riven does not and her back up plan is "don't feed and hope you get carried".

Buying an early goes a long way and stops the snowballing. I found that and all do well against her (at least for me). But never underestimate buying early defense. Like the guys above me said, she has to snowball to be effective. Buying defense early and sacrificing damage will shut her down and help your team to the same effect as getting fed with damage items.

I haven't seen SInged in ages, does he really counters riven or just don't get killed by her?

Not getting killed by Riven is countering her, because she HAS to snowball in order to be effective.

telegraphed knockup, super squishy with no innate sustain other than a shield that has an actual decent cd (she has to build lifesteal which she usually doesn't until after her tiamat and/or brutalizer). You can zone her off creeps with a lot of champs and force her to blow her cd's to farm so she loses kill pressure on you. Fight her when her shield and stun are down, even if she has her Q ready you should be able to out trade her. If you are ranged you can easily harass her down, even as a lissandra your AA's will hurt a ton as she is more likely to shield/dash away from your Q.

She's got a medium-high skill floor if you want to do well with her.

Stomps on her so hard in lane. She has a hard time retaliating. Renekton brings hard CC, which fucks up her combos. 85% of the time Renekton will stomp this lane and make Riven cry

-sincerely a riven main.

Low burst, her combo takes an extended amount of time to perform, very squishy, low shield duration, bad regen.

She's typically relatively squishy, and she doesn't have a huge gap closer like Yasuo ult or something to engage (and using her Q to gap close means she loses a lot of damage). I think her teamfighting is pretty lack luster unless she's really fed, especially if you can poke her out a bit before. She's also pretty bad if she falls behind. Garen also hard counters the crap out of her.

She's one of those champions with insane outplay potential though if you've ever watched Faker highlights or something. She's a really strong dualist, so unless you're playing a hard counter or feel confident in your ability to outplay her (either by playing another good dualist or just being a better player), I wouldn't fight her unless in a clear 5v5 teamfight (she has low cooldowns and no resource so she can do well in skirmishes)

Lissandra seems to do well against her Mid or Top. And Liss isn't that hard to play. Just poke with Q and if she does try to engage you have your W for a small stun, your E to escape and Ult to stun her or yourself. And you can just farm and poke with Q and wait until your jungler comes if you need to that way you can E into her then W and R her.

hard cc like seju/amumu ults, taric stun, etc, just make sure she cant do anything and its quite easy to burst her with her low hp and inability to move.

she also loses to poke and range like xerath ziggs syndra etc, shes reliant on flash/fog of war to get close to these champions so she can only do that so often.

Aside from one of the shortest combat ranges in the game, also has terrible sustain, which makes her extremely vulnerable to poke. Tanks end up out-trading her by stacking armor, and even squishies will destroy her if they pin her down before she can reach them. Her engages are also super-telegraphed, so unless she burns or jumps you from a nearby wall or bush, you're going to see her coming from a mile away.

her dashes aren't instant. she has to do 2 or 3 of those little hops to close the gap, so it's easy to react to it with some hard CC before she gets in range to do anything (contrast with, say, Wukong who can dash->q->ult before you can react)

Descent early game

melts to CC, terrible health regen, is forced to build damage regardless of losing or winning lane, crippling cooldowns before buying CDR, weak teamfight, if she uses her abilities to close in she has nothing else to do after reaching you (hence having to use flash + w then combo you sometimes).

also, high skill cap.