Yeah, I got her right away, and I probably use her more than anyone else on this site. If you want her though, there a few a few things you should know before spending your points. I could go on forever about her, but I'll just give you a short, simplified version:
1. Riven is an early game character, but she has no late game unless you are fed. You absolutely have to be scoring kills to do good late game, or she quickly begins to fade away around level 7.
2. Riven has no AP or Mana. Her skills are scaled off her AD and any AP is wasted on her as she doesnt use it at all. She also runs without mana nor energy, so is solely cool down based. This comes as both an advantage and a disadvantage, as you can concentrate more on stats that matter like AD and Speed, but it makes you easy to counter as you have no way to get around AD Tanks.
3. Abuse her passive. Every time you use a skill, use an auto attack before activating another skill. So if you want to use your whole Q combo, go Q > AA > Q > AA > Q > AA instead of just Q > Q > Q, otherwise your bonus damage is wasted. Remember that this passive also works on her E, so when you throw up your shield you're also getting that buff.
4. Riven can only fight in groups when the enemies are bunched up, if they spread out, she's screwed. She can get in fast, but that forces her to leave slow, and she can only burst a small area, meaning you leave yourself very open if they arent grouped up.
5. Riven is very frail and squishy and she cant win 1 on 1 with most other fighters. She fights by running around and staying mobile, then hopping in for a bit of burst damage here and there, then hopping back out trying to poke and prod while the rest of your team tries to separate and wall the opponents.
6. Riven has a HUGE weakness to any type of CC, she is out bursted late game by most AD champs, she lacks any good sustain, and she absolutely needs to be fed in order to in order to be any type of threat in long games.
So yeah, if that appeals to you, I'd highly recommend her, just be known that you have to be VERY aware with her and you cant play her well on autopilot.