Having now watched it back to back against Casino Royale, I think I can see where it was going (or what they were trying to do).
Remember, Casino Royale was retimelined, need to forget all previous films. And very successfully done too imho.
I think you have to look at the 2 films as one, as as well as introducing 007, it has to introduce a new organisation that Bond has to fight against - remember the Connery (and Lazenby) films were usually fighting against SPECTRE - a (almost) believable global criminal organisation. In Quantum of Solace, I wonder if they are trying to introduce similar with the similar organisation Quantum? Perhaps should have been all done in the one film, but may have been too long then, and certainly too complex. Quantum of Solace has a complex enough plot as it is.
As to the worse Bond film? That surely has to go to Die Another Day. Followed closely by Tomorrow Never Dies...