If you're going to add in plazas, it looks like there's a centralish area with a fountain or something similar that might be great for the "major" one Loogie mentioned. Placements are definitely up to you, but I'd also consider a small one by the docks/wharf area. Since the city is on the river, I'd make use of it. Is it near the ocean as well, or upstream? If it's near the ocean, it might be a trade port, so you might want to develop even more city along the river. If it's further upstream, I think what you have is great.

I love that the city isn't predominantly grid-based, but yet it has at least one or two really big, "main" streets. It looks random enough to be natural and yet not so random that it looks haphazard and just thrown together. I'm envious of your street layout abilities.