The "problem" with the LLVM project is its massive success, coupled with its incredibly difficult problem domain. Turns out it's actually really hard to write modular compiler infrastructure that serves as the optimizer and code generator for N different arbitrary programming languages. The fact that it works in this capacity at all, and still manages to be competitive with GCC in its original use-case (being a C/C++ backend) is a monumental and unmatched achievement.

As someone who works on an LLVM-based compiler at $DayJob and also has written a compiler front-end that uses LLVM in my free time, I do have a ton of gripes, but any time I feel particularly frustrated by them, I spend a little bit of time working on my non-LLVM backend. After a few days of angry swearing with little to show for it, I go back to working with LLVM with a much greater appreciation for what it's giving me.