Water Lily at Longwood Gardens

There's something about this photo that I like. Do you think color

balance, brightness/contrast and artifacts need some work?

No, I'd leave it as it is. I don't personally like too much post processing so I always try to avoid it where possible. The contrast between the colours of the lilly and the dark, almost black water really pulls your eye into the photo. At the same time the lilly pad in the bottom right adds an interesting contrast, especially with its own pattern. The only 'down' to the photo is the rolled up leaf which looks like litter at first glance, and the dust on the water, but if that's what was there when you took the photo, then what can you do?