I think Q of S partnering Casino Royale makes for one of the best Bond double acts of all, at last something much truer to the books in tone, with some clever homage to the iconic old films. I went in a group of people all of whom thought it excellent bar one who thought the film was terrible. On questioning I realised that he just had not understood it, he said this, that and the next thing were unexplained or not clearly motivated, but they were, at least I understood it completely, I was riveted by the plot. I find most criticism is that the last 2 films are not exactly like all the others. I think if you see these movies without such preconceptions then you are pleased with them. If you want to see Goldfinger again, rent Goldfinger.
I agree that it is not a standalone film, you have to have seen Casino Royale, but it is mostly a case of this more cerebral film being too sophisticated and jigsaw-plotted for the admirer of the Roger Moore type Bond films, which are essentially cartoons, and usually with plots so ludicrous or complex that no one really knows what is going on.
Another criticism was that it did not contain classic Bond elements, but it most certainly did from a complete account of what he drinks, to compelling locations, a wonderful villain and beautiful, but more credible, girls. It isn't 1975 any more, Bond has to move with the times, churning out the same thing year after year doesn't work and the Bond franchise has never actually quite done that. I think Daniel Craig is the best of all the BonRAB - he best encapsulates Bond's ruthless killer streak, albeit he is not a public school type with charm, but that's so 50s I don't think you could credibly do that now and keep it popular. Connery had charm which Craig lacks and he also was not a public school type. It's between those two.
All that said, this film surely has the worst Bond song ever written. I assume the artistes paid hanRABomely to have that forgettable dirge slapped onto the film titles.