Quantum of Solace is, as others have said, a direction continuation of Casino Royale. It's brutal, rough, and unrelenting; far more believable than the cheesy corniness of most of the earlier Bond films.

From Russia With Love is, in my mind, one of the better Bonds. Brilliant Cold War suspense, plenty of intrigue, a fair amount of action. Yet still firmy rooted in the Cold War mythos and very much a product of 1960s film production values. It is perhaps more engaging than Quantum of Solace, though that depends a lot on exactly what any given viewer is looking for in a film. I think it's fair to say that QoS suffers slightly from what we can call "middle of a trilogy syndrome", whereby the story neither truly begins nor truly ends. It began in the previous film and will continue in the next; there's not the same level of closure of completeness that you get in a strictly stand-alone movie.

But if you want a Bond who's believable as an ex-military, secret service agent combating believable and plausible opponents, then the new Bond films are right on all counts. No 'novelty villains' with ludicrous super-weapons or freak-show henchmen. Sure, they offer a different approach and a different perspective, and this won't agree with everyone. But if people just want to watch the same old formula again, they've got 20 films from across 40 years to fall back on.