After my last rewatch I would say that the Saiyan arc went from my least liked Z arc to my most liked. It's the perfect mix of the good from the 1st half of the manga with the good from the 2nd half of the manga. Solid enough writing, a wide breadth of contributors/fighters being relevant, fights being more technique based instead of just raw power creep (though you definitely begin to see this becoming a thing in the Saiyan arc), and the alien twist serves as a way to sort of re-open what seemed like a relatively completed character arc in Goku.
With Goku in Dragon Ball it felt like a big part of his character was coming to terms with his own humanity. Having lived in the wilderness all his life so isolated from civilisation, much of the original show in-between the action is basically him sort of adjusting to human society and it's customs. Making friends, learning that there's another sex, figuring out where humanity's social and cultural boundaries lay and not crossing them, etc. Nowhere is this more evident in that one scene where he goes looking for Bulma in West City, IMO.
So him having actually been an alien all along really kind of throws a wrench into everything just when we thought that Goku had figured everything out. Him finding out that he killed his own grandfather is a surprisingly feelsy scene. This ultimately culminates in him fulfilling the legend and taking some measure of pride in his Saiyan heritage in the Frieza battle, which is fantastic payoff. I think this sense of finality for Goku's character is why that old myth about the show having been supposed to end after the Frieza arc became so popular in the fanbase; it just
feels right. Though I love the Cell saga as well.
But anyway, in my opinion the Saiyan arc has all of the good of Z; the fantastic action and fight choreography, constant power escalation and the highest stakes the series had yet seen while not suffering from the asspulls that subsequent arcs do. Like the zenkais/random power boosts on Namek because Tori wrote himself into a corner with the power levels and needed to keep the characters growing
exponentially in strength to justify the numbers, or all of the time travel nonsense and characters acting like retards in the Cell saga, etc.