I'm playing devil's advocate here, as some of my choices I personally think are great, but:-
Over-rated - any Connery Bond film, purely because for decades, in the opinion of many - especially film critics - a Bond film wasn't a proper Bond film unless it had Sean Connery as Bond, and the Connery films were viewed as superior to the rest. Even the ones when he appeared bored in the role. And I type this as a Connery-Bond fan. But to write off the efforts of the successor Bonds in this way isn't right, in my view.
And as a Craig-Bond fan also, it will be interesting to see if, come Bond 24, there's a backlash against SF. As one poster put it above, fickle fans tend to show their love of the new by hating what came before it. We've seen that when a new man takes over as Bond. Remember the welcome Pierce Brosnan got after taking over from the "dour" Timothy Dalton? The same Timothy Dalton who was praised by the critics for his performance in TLD?
Speaking of TLD - overrated to underrated - The Living Daylights. When I first saw it in 1987 it was highly regarded by fans and film critics alike, it seemed. When it appears on TV now, its ratings are routinely put at two out of five in the Radio Times film listings, for example, with one critic complaining that Dalton had phoned in his performance.
Underrated - OHMSS, still. Diana Rigg gets praise, rightly, but George Lazenby still gets stick for not being Sean Connery. Roger Moore's first two Bond films, particularly TMWTGG. Yes, it's got Britt Ekland making a fool of herself, J W Pepper making an unnecessary return, and the car corkscrewing over the broken bridge is daft. But it also has Moore-Bond in some uncharacteristically hard edged scenes, the dignified but doomed Andrea Anders (Maud Adams), and best of all, Christopher Lee as Scaramanga.
I'd also add that with the exceptions of TSWLM and MR - which are routinely praised as spectacular and fun - most of the Moore Bond films are underrated, imho. True the style of humour wasn't always to my liking as a fan, but they were entertaining and had plenty of Bond style moments.
Finally, and getting back to the Dalton era - LTK. Lost in the hype surrounding other 1989 blockbusters, not well promoted, and harmed by the writer's strike of that year, LTK was a daring attempt to do something more hard edged and realistic with Bond. A prototype, over a decade ahead of its time, for the extremely successful Craig series of Bond films, perhaps?