Leone's sequel goes the route Evil Dead 2 would later take of bigger, better, funnier. This is so broad you could be forgiven for thinking it's a pure comedy at times. Leone's as likely to stage a duel for laughs as for drama and tension.
Eastwood's Manco, mostly taciturn and grim in the original, is now slightly less taciturn and decidedly less grim. Sometimes this is just a result of the surreality of a scene (his visit it to Old Prophet, whose shack must be mounted on a moving stage; all Eastwood can do is ride with it when a train goes past) but mostly it's due to having someone to bounce off in the form of Lee Van Cleef's wry and quietly confident Colonel Mortimer. One of the comedic highlights is their dust-up in the street, as each outmatches the other in hat shooting gunplay.
Morricone delights in punctuating these moments with almost Carry On... level sound effects (except much more inventive ones that are germane to the overall score); both the scenes involving Mortimer and Klaus Kinski's hunchback see Van Cleef out-cool anything Eastwood is given (although Manco's final line, "Thought I was having trouble with my adding. It's all right now" is a lovely lead-out).
I'm not sure there'll ever be a more perfect marriage of visuals, editing and score as between Leone and Morricone. The climactic duel between Mortimer and Indio is a composition of beauty, reaching a crescendo of image and theme, expanding mere moments to minutes (the pocket watch theme is the highlight of the soundtrack); and then Leone goes and tops it in his next film.
Mario Brega's weed-smoking psycho Indio is so far over the top he could only work in a film with this kind of heightened sensibility. The discordant strings Morricone uses to show one of his moods coming on are simultaneously hilarious and disturbing. Manco and Mortimer refer to each other as "old man" and "boy" respectively, but there was only five years age difference between Eastwood and Van Cleef.