On the one hand, if it's genuinely self-contained (that is, it doesn't expect a .Net runtime to have been preinstalled on the OS), that may well constitute an improvement over previous iterations of C#.
On the other hand, the smallest executable I can find on my system occupies 6K and actually does something useful.
On the third hand (said the octopus), if all we cared about was executable size and efficiency, we'd still all be coding in assembler, or at least C or Forth.