Most specifically, I dislike its middle three letters. The problem with OOP is that it requires to know exactly what ones want -- it is difficult to change the design of your program after it's been written (and it is also difficult to come up with a good design from the beginning), and -- since it is based on state mutation - it makes it difficult to reason about your program.

On the practical side, it was a bit counterintuitive that <uvec> and <vector> were unrelated, and I think that there were some issues with <pair> and <list> types.