Played Nitro a couple times and I think I have a handle on his kit and the idea behind it, but I find him exceedingly weak:
So Nitro is incredibly fragile and I feel like her stats still expect her to have a 1500 range and evasion. She now has neither and, especially with her Q, is expected to be up close harassing. This is incredible dangerous for her as her Q is not a deterrent in contrast to a hero such as Arachna, who's orb slows hard AND has a DOT.
Nitro's Q is cheap and allows her to attack under a tower, through a creep wave, etc. However, the shrapnel left behind is very hit or miss, because the variable range they appear at makes it hard to force opponents to walk over it. From what I understand, the idea is to lay down tons of shrapnel, then chase opponents away over the shrapnel or use W to force them on it. Interesting mechanic, but in such a movement-focused game, it's very hard to put this into practice or lay down enough shrapnel to not have it absorbed quickly or eaten by creeps.
Furthermore, the variable range gives it a decent chance of hitting creeps, thus pushing the lane when you may not want to.
I hate her W. As others have pointed out it is super hard to hit close enemies, thus negating a lot of its defensive use - getting attackers away from a glass cannon Nitro. Secondly the targeting is very short range and has too much of a cast time. An opponent in the middle of the cursor can easily walk out of the blast area before it goes off.
I do have a suggestion for this though - Artillery used to have a similar ability, but it would push him away rather than the opponent. The targeting was a circular AOE reticle and was much easier to land. Perhaps Nitro could use that instead?
Underwhelming. The speed boost is very meh. I understand it should synergize with keeping people in her ulti, but it doesn't help when the real issues are stuns and slows rather than speed. Also, the active is slightly useful for getting to a gank, but she isn't a ganker, so I don't really understand the point. Also, why should it slow down around opponents? A good move, imho, would be to add evasion onto the ability as an active that gives 20/30/40/50% evasion for x seconds. This would allow her to focus on maneuvering while using her ulti, rather than running away from opponents.
Interesting ability, I love that she can move while firing. However, enemies can juke, go invisible, stun or get out of range to nullify it completely. Also, if you get stunned, you have basically wasted it. Finally, it seems to force Nitro into going for modifiers or proc items, but they leave her so squishy that following someone with her ulti is pretty much an instant death.
Would love to discuss further.