After working 4 years on C?
Is it good? Not necessarily. Working in kernel requires good understanding of the operating system and programming. If you make any mistakes there, there is no one to catch them. Your whole system will come crashing down. Having said that, is that an exciting place to work? absolutely. It all depends on your interests. But do remember that unless you are very good at what you do, your career in kernel programming will be short lived.