Nice framing but I would like to see where he's landing...
A lot of bmx, skate, inline, shots that I see never include the landing. IMO when the landing is included in the shot it completes the image, it tells, and finishes the story as a picture would tell it. When you just catch the trick and don't leave the viewer with the landing for reference, it makes the shot kind of flat.
I'm not trying to be negative, just constructive. I think your photos are fine, just try including the landing next time and see what you think.
I think Tim's right about the landing. Now just to take this in a different direction... how about a small remote flashs @ camera left? I think it would just make the shot pop with that evening light falling off.
the timing on the shots are a little early. you want to capture the moment when the skater is at the peak of their arc, and their legs are all styled out. it's something only a skateboarder would notice, but i'll make a difference in the images. what other people are saying about showing the landing is true. that being said, i really like the composition/color on the first one. the second one doesn't have anything going for it.
I like the first but the second really isn't doing anything for me. Needs to be wider and preferably needs some flash on it to brighten the skater up and make him stand out.
I'd also echo what Rowan said about timing on the shots. I think on the first it is actually good that you got the shot early but on the whole, top of the arc is the best moment.