I also haven’t watched the Creed films, and that gives me pause because I wasn't even aware of them until after they came out. So I can’t really offer an opinion on all the Rocky movies at this point... However, I think Rocky II marks the spot where the series took a turn; it was the final truly great installment. That isn’t to say I dislike the subsequent films, but something changed for the franchise after that one. The first two movies focused more on the characters and their connections within that world (though Creed felt somewhat lacking in development in the initial film). Rocky II compensates for this, allowing you to get to know Creed as someone who initially appears superficial and boastful, but is actually a person of depth and integrity. You see that other side of him during the final fight; he’s more than just surface-level showmanship, and Action Jackson delivered an excellent portrayal of it, largely through nonverbal cues at the very end. It's genuinely a satisfying performance. It’s also a performance that fully develops his character to the point where you can accept his actions in Rocky III. This works well with Adrian (who unfortunately became a less significant presence after II), Paulie, and Mickey. Ultimately, what you are left with is the last truly memorable Rocky film centered on characters before the series began emphasizing boxing itself, only to eventually return to its focus on Balboa.

Source on TMDB