If I had to summarize what specifically could be improved in Debian, the only thing I would do is rolling release, as some other operating systems are doing. I can see why they do not do it, but I can also see that it would be helpful so that if there are things done better in a newer kernel, that could be integrated in quicker. I usually build my own kernels to suit specific applications for specific customers, and it pays to do that anyway with any Linux. I find Debian tends to have all of the switches available in their kernel build so that you can turn features on or off, include them, or leave them out, whatever you need to do.
