Oooh, Changi Boardwalk is a popular haunt for photographers. Good location choice, though a tad cliched. (or maybe I've seen one too many CBW pix... haha)
I find a portrait shot to be an interesting idea- there is no rule dictating that beach-y photos HAVE to be landscape-oriented. This is refreshing and different. I like! (Also, I know you have a reason for taking it in a portrait-orientation- the focus is on the man and the tree, not the rest of the ocean, right?)
What I think can be improved on, though, is the composition. What you have here looks like a hamburger- the top bun, the patty and the bottom bun. Hamburger pictures are not really aesthetically pleasing (at least to me), because there are too many areas of focus. What would make the picture great, imo, is if you have a higher back/top ground and little or no foreground (crop out the bottom). I've cropped the bottom out here, so you can get a general idea of what it can be like. This crop is by no means an alternative, because it's too compact as it lacks a good top/exposure of the sky/sunset/whatever.
This way, you can have a long photograph that is somewhat emotive with the man in the foreground by the silhouette of the tree. I can imagine it being a great picture like that. (I also like the idea of making him face his back towards you- it would make him appear more contemplative, like others have suggested)
Oh oh!! One more thing.
A longer exposure time will make the water less crinkly, and more smooth, giving it an ethereal effect. That will greatly improve the aesthetic quality of your photo, methinks.