Hmm....one thing I've always found frustrating is that Riven can be extremely tanky and resilient with zero defensive items built. Largely because A) she has a shield that scales off of AD, which is never a good thing, and B) she has a stun whose damage is also based off of AD, with very little counterplay aside from flashing away before she dashes.
I want to propose two possible ideas. The first is making her shield scale either off of bonus health, or not at all (a la Jarvan's shield ability), and having her stun damage either AP based or bonus health based. Anything that takes out free power scaling from building nothing but AD is a plus for Riven.
Secondly, her charge system. Right now, she is encouraged to use her abilities to stick to people, because abilities make her autoattacks more effective. Since her abilities are on such low cooldown, however, this doesn't really feel rewarding so much as free extra damage that's up all the time. What I would propose is that the charges go THE OTHER WAY. Here, autoattacking would build her charges, and her abilities would be more effective based on how many charges she has. They can still be used without her charges, but, say, her oh-so-exploitable stun would be a slow if you used it without any charges built up, but would stun people when you have charges built up. Every use of an ability would absorb one of those charges, and the power of the ability would depend on how many charges you had when you used it. The exception to this could be her ult: it will absorb ALL the charges, and during her ult (until she either releases it or it just wears off), all her abilities would function as if they were used at full charge capacity, or at the charge capacity she was at before her ult. This way, the charge-building mechanic she has would feel a little more rewarding, I believe, and more like a bit of power that you worked hard to build instead of just...free autoattack damage when you spam your abilities.
So, for example, lets say the cap on your charges is 4. You've just last-hit four minions, so those charges are available to use. You dash, giving you a sizeable shield (max charge level), then stun for a decent amount(level 3), then do your three Q slashes (which absorb only one charge total, level 2). In this example, the shield would've had the strongest "charge" scaling, since it was used when you had 4 charges; it then absorbs one charge. Unless you auto-attacked before hitting the target, the stun would have had a third-level "charge" scaling, and so would've stunned for a good bit of time, but not as long as if it was used at max charges; another charge gone. Next, the three slashes with Q would've done decent damage, but it would NOT burst someone down too quickly, as it was used with only 2 charges stored; now you're down to one charge. Here, you could potentially ult, but if the ult is modified to follow all the other ability patterns, it would only have a 1-charge effectiveness; all abilities used during ult would only be as effective as if you had one charge built, and no charges are built or consumed during ult. Might possibly make ult either automatically place you at max charges, or give two charges when used.
The charges would have to have a LONG duration on them, so that you could, say, max it out doing red buff (if you wanna try jungle Riven), then walk down to bot/top lane to pwn somebody. When they DO fall off, they do so one at a time.
