Pretty versatile. It has some weaknesses, such as no runtime type protection, but you can do object-based programming, some object-oriented programming, block-structured, and regular old procedural programming. It interfaces well with tons of other languages. It's about as portable across platforms as Java is, which is to say you still have to be careful about hardware-dependent stuff. I'm aware of no compelling reason why a legacy project which is already in C should be rewritten in another language.
That said, I personally would never in a million years choose to start a new project in pure C unless the only other option was assembly (e.g., writing hardware drivers or software for NASA satellites with special hardware). The lack of runtime type safety makes me nervous (I'm counting things like dangling pointers as a type safety problem here), and it's also a rather verbose language. There's pros and cons, and I'm turned off by verbosity in the same way that I'm turned off by nations with capital-only mages. There, back on topic.
-Max