1. Sean Connery: He gives his definitive performance as Bond, layering it as well as anyone since. He's tough and resilient in the underwater battle and chateau fight and shows the human side of Bond quite nicely in the beach scene with Domino. The close up of his hand trembling slightly as he gives Domino her brother's watch and ID tags is all you need to know in the scene, acted to perfection. There is also the great transition from nice guy to killer when Vargas approaches.
2. Adolfo Celi: Jim has brought it up before, but Celi's performance as Largo is truly one of the best villains in the series. Rather than a megalomaniacal lunatic hell bent and insane, Largo is cool and methodical with a strong streak of cruelty that makes him viciously chilling.
Another aspect to him that i'm not sure has been touched on is his similarity to 007. Both men are professionals who are willing to do anything to get their respective jobs done. It can be said that Largo is the first instance of a villain who is the dark side of Bond.
3. The Editing and Music: Peter Hunt and John Barry do their usual brilliant jobs but the bit I've always been thrilled by is the fight on the Disco Volante. It's one of the best five minutes of film I've seen and really warrants closer inspection.
The music starts us off right, transitioning from the lyrical underwater theme to the pounding rendition of the 007 Theme. From there, we get Domino being set free in two short scenes that play out in short movements, just long enough to relay the needed information. The ensuing fight is great as Bond and Largo fight for control of the steering wheel. I'm especially fond of the shot where Bond is steering around the rocks. Connery sells the moment brilliantly.
As for other elements, the film was marketed brilliantly, building on the success of Goldfinger by touting the next film as even bigger. Thunderball is not without a few flaws, the missile theft scene could have been dealt with a little faster while still conveying the idea of the scene but really it's a minor flaw.
There are so many great elements in the film it's almost impossible to cover them all. But hey, life is full of small challenges, eh?
