The one thing that jumps out at you when you watch a bunch of James Bond movies is how few of them really can be called good movies as a whole. Most of them have some memorable scenes, or memorable stunts, or something. (Even a turkey like Diamonds Are Forever has the justly-celebrated scene of Bond getting his ass kicked by women named Bambi and Thumper.) But because Bond movies are entirely a collection of set pieces, with just a hint of plot to get from one set piece to another, most of the movies don't really have any individual identity. It's like a variety show; you remember individual sketches, not whole episodes. The only movies that have some kind of cohesion are the ones that are actually based on the Fleming books, like Goldfinger (which is in this set) and Dr. No, From Russia With Love, On Her Majesty's Secret Service (which aren't).
Thunderball is sort of an in-between film -- a little more cohesive than most Bond movies, less cohesive than the first three or OHMSS -- but despite the weakish head villain (Adolfo Celi), I kind of like it, as it was one of the first Bonds I saw, and it was probably the last film to preserve some degree of Spillane-esque nastiness in Bond. (On Her Majesty's Secret Service is great but George Lazenby isn't exactly menacing.)
But the other thing that jumps out at you when watching a '60s Bond film like Goldfinger or Thunderball is how well-dubbed they are. Many movies, especially big productions with international casts, were at this point shooting many scenes without sound and re-dubbing actors who couldn't speak English. (Or, as in the case of Shirley Eaton in Goldfinger, didn't have the voice the producers wanted for the character: so they combine her body with a different voice to get the composite character they were looking for.) A lot of this dubbing, especially in American movies, was very obvious and distracting, but the dubbing in the early Bonds -- mostly supervised, I think, by the editor, Peter Hunt -- mostly sounds like it's taking place in the right acoustic for the scene and sounds natural coming out of these characters; even when Sean Connery post-dubs his own lines, as he frequently does, it doesn't sound like ADR unless you're really listening for it.
Finally, I put the question to you: which Thunderball song do you think is better: the original, "Mr. Kiss Kiss Bang Bang," or the title song that the producers made John Barry write and record as a replacement? I have no problem in saying that I prefer "Kiss Kiss Bang Bang," mostly because of the lyrics: the lyric of "Mr. Kiss Kiss Bang Bang" is one of Leslie Bricusse's better efforts, whereas the lyric of "Thunderball," by Britain's worst lyricist, Don Black, makes absolutely no sense.
Version # 1 ("Mr. Kiss Kiss Bang Bang")
Version # 2 ("Thunderball")
Update: A commenter asks why the song was replaced. John Barry explained in an interview:
The Bond team had even chosen the singer - Dionne Warwick, who sang her own arrangement, after Shirley Bassey's original version had failed to impress. Barry takes up the story: "Dionne's was a marvellous song and she did a great arrangement for it. It was a really strange song. I had about twelve cow bells on it with different rhythms, along with a large orchestra, and thought it a very original piece. Then, at the last minute they got cold feet and decided to have a song called 'Thunderball'." The official reason for the change of mind was that the original song-title may have been considered to have sexual connotations in conservative America, but rumour has it that there may have been a threat of court action from Bassey following her replacement by Warwick. Obviously if the song wasn't used at all, there could be no case to answer!