I'd like to see some red in the background. You have it in the foreground, with your crypt, but it gets lost in the shadows. You're providing background splash with the lighting behind the tank. I like the effect, but thats cheating.
I know how you must have that feeling like your tank is stuck in the doldrums, but I think strategic addition of several new plants would give it life in your mind. You've been looking at the tank for a long time, we've seen it since two days ago when you posted the pic.
As cs Gardner said, it has a wild look about it. I'm assuming you don't want to change that. It fits in this case, so I would be minimal with additions.
I'm sure someone will suggest a white or black background, so I'll beat them to the punch. Try it by taping trash bags of various colors on there and see if it improves. I don't always like the way a background looks, and this way you can decide to/not to do it without being out a bunch of moolah.
I see a texture divide down the middle of the tank. You have wide leaf plants on the left side, and narrow leaf plants on the right. If you were trying to achieve that effect, you succeded. In a wide tank like a 55, I like to see a variety of things depending on what side I'm looking at. I know I did something similar when I had my 55 running.
However, in a photo it looks slightly affected.