Riven: Why Call Her OP? -or- Would Like Advice. PLUS General Playstyle through Forum Link

I'll be brief: RIven is considered as OP and broken. But this is only true if she gets ahead. Whenever I've played Riven, or tried to play as her, she gets stomped on in lane and can never catch back up.

Thematically, I like RIven. I like the idea that I could dominate with her, as I've seen many times. But the skill I may need to play her is just horrible. She has no innate sustain, her HP5 is almost nonexistent, most of my lane matchups in top countered her by poking at range or mitigating/healing up her damage, so I could never really harass anyone or just farm for my core items. Building tanky/defensive early on may be safer, but it delays my ability to do anything so badly.

That said: I could use help in giving me an idea of what to do with her, assuming that I use her in a Team Builder setting where I have no prior knowledge of who I will lane against. I'd also prefer not to see "Don't fall behind ever" as offered advice, since I'm looking mostly for fallback strats as Riven and not an assumption that I must do well or abandon the game. If such IS the case, then present that point in detail and suggest either how to practice Riven (not just where, like "in Bots"), or a different champion that better fits my playstyle that I don't already play a lot, preferably someone I own. And please, for now, NO suggestions for Boxbox streams, either; unless Boxbox has something that step-by-step explains what to do as Riven in any situation good or bad, then I don't consider streams as the be-all and end-all of learning something (now watching the LCS matches, I have picked up ideas of what to do in general situations as any champ, but that's a different story). The streams for Boxbox I've seen so far are just her playing Riven in various competitive matchups, and I lose track of what happens in the thick of it.

This ties into my earlier post http://boards.na.leagueoflegends.com/en/c/tips-tricks/aTd5vZpy-looking-for-champions-i-would-do-well-with. Give it a spin, proffer your thoughts based on the presented material, and I'll see what else shows up.

ALSO: in terms of ranked play, I finished season 4 at the bottom of Bronze 4, mostly from losing streaks. Currently I'm in placements, six of ten, four wins two losses, possibly ending up as Bronze 4 again. I started playing Vi a couple of months ago, absolutely love playing as her in the jungle, but have been falling off a bit with her; was at an almost 70% win rate, now slightly above 50%-ish.

ALSO ALSO: So much for the "brief" part. :P