I have fairly limited experience with her so far but from what I can tell I find her to be unique and fun to play, while being a strong asset to the team. I do have a few concerns/suggestions, however:
1) I find her passive is oddly clunky to use for a few reasons:
- The full-speed-boost for a very small duration makes it very hard to make use of. I'd love to see a longer duration but have it do that "falls off over time" thing like shyvana's W.
- I find there's almost no time you would ever use her E to proc her passive on someone (the only time would be to run away, but you already bring enough CC that the tiny move speed boost is pretty negligible). If your target is a ranged champ, the slow from the E procs makes the move speed from the passive seem irrelevant. If your target is a melee champ they don't really benefit from the move speed because melee champs almost always have gap closers anyway.
- Proccing it with her Q seems awkward. Proccing it with her R will happen every teamfight, but it almost seems pointless because her passive already has a crazy potent slow (70% for 3-5 sec is amazing). The only spell I see a Nami ever casting specifically to proc the move speed will be her W seeing as you can use that to hit it very reliably on two allies.
- I'm NOT saying her passive is bad or that her abilities are bad. I'm just saying that I really feel like you will almost never say "I want to proc my passive on x player right now", and the rare times you do I'm betting it'll always be her W that you use to do so. I think it would be a much more interactive passive if it was a stronger boost initially but falls of very quickly over 1-1.5 seconds instead of a flat mediocre increase. If that was the case, you could use it for clutch repositioning in fights.
2) Not Nami-related per se, but I'd almost love if more spells that had strong CC effects (Nami's Q) had a medium to high base damage (for laning presence) but literally no AP ratio. That way they could truly tune the skill all around its CC and per level damage and not have to worry about someone going AP mid with them and being broken.
I'm not saying "supports should not have AP ratios", I just really think it would bring an interesting dynamic to the game if hard CC abilities were more base-damage and CC focused rather than also having high scaling on them.
Not sure if that could work at all because I have no experience designing complex games like this (the most I do is basic 2-d side scrolling games :P), it's just some food for thought.