I'll say the arcs I enjoyed the most, praising them and then criticize them.
-Frieza arc:
Praising:
The lead up to it was fantastic(The whole saiyan arc, it's the only thing in Z that feels like a series of events as almost every other arc is self contained) and it was really nice to see the Z fighters being the underdog and use their wits to stay low. The villains were entertaining, especially the Ginyu Force, and It also has plenty of good fights and who could ever forget the legendary Super Saiyan transformation? Definitely one of the franchise's highest point.
Criticism: I'll start by getting the elephant out of the room; The arc drags on for too long. Yes, you could argue almost every other arc does but the Namek arc somehow manages to be slower. Maybe it's because I watched the anime instead of reading the manga. There's a reason the "Are they still on Namek?" meme exists. Also, the whole fight with Frieza kind of just becomes stale; It's a Frieza unveils new form, overpowers the heroes before he gets overpowered and has to turn into his next form, rinse and repeat. The fight takes a fresh breath of air when Goku returns, but even then, the fight was mostly Frieza overpowering Goku before Goku turns into a super saiyan and overpowers Frieza, but the last bits of the battle were pretty good...Which brings me to my next point; Goku vs Frieza was long as hell, goddamn. It's still to date the longest Dragon Ball fight, it could literally be considered an arc of its own.
-Cell Arc:
Praising: Introduced the concept of time traveling which added a layer of world building to Dragon Ball. Also introduced some of the franchise's most beloved characters, Like Trunks, 18, Cell. Cell is a pretty dope villain and to this day, still one of my favorites ones. Also, The Cell arc has a payout, and that is Gohan where he finally realizes his potential. The Super Saiyan 2 transformation, at least the Japanese one, Is my favorite scene of Z, and a contender for the franchise as a whole.
Criticism: The way the time travel was introduced was somewhat poor and confusing, but then again, plots with time travels do tend to get confusing. The whole arc feels like directionless; 19 and 20 were supposed to be main villain. Nope, turns out it's 17, 18 and 16. But wait! There's another time machine, and Cell shows up! However, it's not too big of a deal because like I said, I love Cell and also, Toriyama was forced by his editor to change villains, so, I'll cut some slack on him. But the other issue is, Gohan himself. While I did mention him as a praise for the arc; The path Toriyama took with the character to get there is frankly inconsistent with Gohan's prior characterization. He comes out as a pacifist, even though a few episodes earlier he was willing to go and fight Cell. It does make sense he doesn't want to go out of control since he's scared of his own power, but that's not inline with the prior occassions where he did so. Did he harm anyone else than Raditz when he first showed his power? Did he attack someone aside Frieza back on Namek? If he did, then the transistion to him being a pacifist would have been far more natural. I would have even taken him using too much power against Goku back in their training and maybe that's why he scared he'll snap out and go out of control. But nope, he doesn't, the change he has comes off as jarring. Still, The Super Saiyan two transformation was excellent and a good payoff to his build-up.
-Buu arc:
Praising: You may believe it or not, but this is actually my favorite arc of Z, and overall one of my favorite arcs. The fights of the Buu arc are on average better than anything else, even if the story wasn't up to par. It also introduced key elements of the Dragon Ball franchise including but not limited to: Super Saiyan 3, Fusion dance, Potara. It also expanded a lot on the world building, more than either Frieza or Cell did. Buu had his ups and downs, but he served a great role as a villain. Fat Buu looked like a bumbling idiot but the guy killed half the cast. Super Buu and his forms were great and did a really good job at being menacing and frightening. And Kid Buu...he was the perfect final villain Dragon Ball could have. A pure engine of destruction, could not be bargained or reasoned with unlike any other villains. The Super Spirit Bomb was also an excellent way to end the arc and the series as a whole; Not Goku who saved the Earth, but the people themselves. And another point I'd like to add is, I like how it avoided the usual route of "New Super Saiyan form gets introduced and the villain gets defeated by it."
Criticism: The whole arc has subpar plot writing. Not that I expect magnificient writing from Dragon Ball(and I really don't, despite that it is my favorite series as a whole), but even by dragon ball standards, the whole arc falls off. It feels even more directionless than the Cell arc. And also, Gohan's character was squandered here. Yes, I know Toriyama planned for him to be the hero but ultimately thought he wasn't fit for the job, it feels like Gohan did Jacks**t. Goten and Trunks were promising too, but ultimately, they amounted to nothing. I would have rather them contributing to Buu's defeat and Goku would be the one to finish the job. I guess we had that technically in the super spirit bomb. And even though I mentioned Super Saiyan 3 not beating Buu as a plus, The form kinda feels like a waste.
So yeah, that has been it for the Z arcs. I could go and talk about Dragon Ball, Super and even GT but I'll leave those for later. And if you read the essay I made then thank you for having the patience to do so.