I don't really dislike gdb per se, and it worked well enough for the tasks I used it for, but I just have a personal distaste code conventions of gdb, gcc and other huge GNU projects. I tried spelunking around gdb source to get at some OS X-specific features and tried adding simple instrumentation to GIMPLE trees in gcc's implementation, and both experiences left me with a negative opinion of GNU coding conventions and showed both projects' age. Looking at LLVM source and following their mailing lists is anything but, showing clear direction and clean implementation. I'm not a compiler guy by any stretch of the imagination, but LLVM felt very well-architected and modern.
Apple sponsored LLVM after I started following it, so while it's true that they are behind it, it has very little to do with my respect for it.
LLVM is a substantial and fantastic project. At the basis, it's a compiler backend in-a-box. Additional projects, like clang and this, are providing a modern compiler platform for us, finally. gcc & friends have made great advances, relative to other compilers, but they all do suck.
It's been 12 years and I still can't use C++ in a debugger without jumping through stupidity. It's literally easier to look at a type definition and read the memory out of a hex dump than go through 16 dropdowns of BS subtype definitions.
They employ around two dozen LLVM developers, comprising half to two-thirds of the regular committers.