All right, let's see. I think the biggest issue is a lack of implied depth to the tracks--the current sprite looks colorful but flat, sort of like the trail in Rainbow Road. I think you'd want more outlines inside the tile itself to fix this--not necessarily surrounding each board completely, but at least enough to imply shadows and make the edges less of a perfect straight line.
I don't know if it's a trick of the eyes or not, but the triangles in your tiles look like they follow more of a rounded sine wave pattern than like they're straight boards. I think the path to fixing this would be either making the lines thicker, or dropping the triangle pattern of the original and making them steep trapezoids, on top of the stuff about outlines for shadow. This is one of those things where I'd need to get my hands dirty myself to know for certain.
The blue yellow purpleish colors, together, are a little outside the GBC Zelda style, which tends not to put wildly different colors together in one tile unless one is the off-white highlight it likes to use. (There's a few exceptions to this, like those flower patches, but they're rare.) This also applies to the train sprite's bright primary colors--they're pretty, but they don't feel Zelda.
I hope this was useful, feel free to ask for clarifications if I got too vague anywhere!