Spectre was a disappointment, I hate to say it but it was. Skyfall would have made a much better exit for Craig but that's the wonder of 20-20 hindsight. That's not to say Spectre didn't have a lot going for it; great cast, Director and crew, even the new look Blofeld was a good idea, Christolph Waltz was excellent. The idea that Blofeld was behind everyone responsible for everything in all four Daniel Craig movies was a bit of a stretch, that and his Daddy issues. It worked with Quantum because Bond wanted to tear down the organisation responsible for backing Le Chiffre and Vesper's murder. But Spectre backing Quantum and the independent Silva (Skyfall) as well? Why did the Producers want to tie everything in a bow like that? By far the biggest issue with Spectre is the ending! Firstly, Madeleine walking away at the point she did and being captured was painfully obvious, the escape from the old MI6 building was questionable but it was classic Bond, shooting down a helicopter flying over central London with two handguns at 200-300 metres whilst standing on a speedboat racing down the Thames was ridiculous. But the cherry on the cake was the final moment on the bridge! I don't care who you are, you would have taken that shot. You have a licence to kill, you shoot him in the head and walk away with your new girlfriend happy in the knowledge that the uber criminal with infinite resources won't ever come looking for revenge. That scene was designed purely to leave the story open for Blofeld's return in the next movie!
Now if Daniel Craig does do one more movie, make it a brilliant one, let him go out with a bang and come back in a few years with a new Bond and some new ideas. However, if he is done, leave it a few years, find a new Bond and come back with something new. No need for a reboot or origins story, leave Casino Royale alone, one era of Bond has ended and another begins. Don't start asking questions about how he quit in the last movie and is now back, by that logic you would have to question how Bond has been around longer than Doctor Who and continually aged and regenerated his youth over the last fifty odd years, much like the Doctor!