Completely agree. Michael Corleone is my favorite character in all of cinema, and Pacino's performance is the greatest acting performance in history. I prefer the first movie simply because of De Niro's scenes, while he did a great job and they did provide a lot of insight into Vito, I just cared a lot more about Michael's journey. In Godfather II he really does make the complete transition into a monster, and it's brilliant. And to say that De Niro was better than Pacino in this is blasphemy. How Pacino didn't win the Oscar for this is outrageous.
Choose life. Choose a job. Choose a career.

If Vito had gone to Ciccio and decided to forgive him due to his satisfaction with his life, it would have provided a must stronger juxtaposition to Michael killing Fredo and Roth for solely revenge purposes.
This is a Karate dojo not a knitting class!!
Sorry, couldn't resist. This is in fact a movie about the Mafia. It's not like Ciccio stole his scooter or took his father's job: he killed Vito's father, mother, and brother. If he managed to catch him, it was his intention to kill Vito as well.
I'm not a big fan of violence and revenge, but Vito's revenge on Don Cheech is quite satisfying in the same way that Capt. Hadley beating Boggs in Shawshank was.
Is very bad to steal Jobu's rum. Is very bad.

I understand your point about Vito whacking Don Ciccio. It is eerily similar to Michael's decision to eliminate Roth despite being in federal custody with only a few months to live. Neither, at that point in time, was any threat to the respective Corleone. When Ciccio eventually croaked, Tommasino probably would have succeeded him anyway. I guess Vito and Tommasino did not want to wait that long.
"Simpsons did it! Simpsons did it!"

I feel like I would like Vito's story better if he hadn't avenged his mother by killing Ciccio. Vito never seemed to be someone who reveled in revenge, including in the first movie. He only killed for business and mostly stayed out of the dreck involved in the mob world, including th heroine trade. He seemed to be someone who prioritized family over business, and to me, the real conflict of the first Godfather is blurring the line between what immoral acts you commit in the name of family and morality, and what you commit in the name of business and greed.
If Vito had gone to Ciccio and decided to forgive him due to his satisfaction with his life, it would have provided a must stronger juxtaposition to Michael killing Fredo and Roth for solely revenge purposes.
There also just seems to not be enough to the Vito story for it to warrant anything in and of itself, again except for serving as strong juxtaposition in other scenes. I maybe wish there was more of a transition to the first movie, as other commenters here have mentioned.

I just prefer Vito more as a character. While Michael's story is more compelling and tragic, Vito's is more pleasant. He is the underdog that made it, the classic rags to riches story. Yet through all that, he stayed true to who he was and maintained principles which few could do in that business. You see how the people in the neighborhood treat and respond to Vito and how respectful he is in return. The fruit vender scene is a good example. Whereas Michael seems to repel all those around him, including his own family. It's hard to watch at times. The end shot of him sitting on the bench is heartbreaking and is a microcosm of his whole life. He was always alone and will always be alone.
Vito, as despicable as he can be, is portrayed as the hero (or at worst an anti-hero product of his environment) in his respective story whereas Michael is the oppositea ruthless, cold-hearted monster.
With that said, I do agree with your point considering DeNiro's performance. It was good and I feel many believe it was as if a young Marlon Brando had played the part. But to me, it was one good performance in a film where just about every performance was good. For me, the standout performance of the film was John Cazale.
"Simpsons did it! Simpsons did it!"

in the book Luca got someone pregnant and after she gave birth he threw the baby into a furnace
Luca also sent a "message" by tying two of vito business rivals up, then he chopped one of them into pieces with an axe while he was alive
the other one watched and screamed
he was told go home and tell your boss what you saw

I would have liked to have seen the Corleones during the Olive Oil War. It would give us an insight into how a younger Vito handled war time. It would also show how a wartime consiglieri (Genco) advised the Don properly. Think of it as a parallel to Sonny/Tom's handling of wartime in Part I.
Also, this is where the relationship between Vito and Luca would be more prominent. We would get to see why Luca respects and fears Vito as much as Vito feared and respected Luca.
"Simpsons did it! Simpsons did it!"

They could also include a few scenes showing the progression of Clemenza's voice changing.
[rimshot!]
Is very bad to steal Jobu's rum. Is very bad.

I love the whole prequel part and would have preferred a full movie based on that then what GFII ultimately became.
I thought it might have been interesting to see more of the intervening years between the end of the prequel and the beginning of GFI. Perhaps a few scenes of the early days of Luca Brasi, Johnny Fontaine, and the infamous "Bandleader."
They could also include a few scenes showing the progression of Clemenza's voice changing.

I'm not challenging anyone, I would just really like to know someone's opinion on this.
Don't worry about what everyone says. You know what you like and that's how it should be. But:
Count me amongst the "young Don" DeNiro scene fans. I love the whole prequel part and would have preferred a full movie based on that then what GFII ultimately became. This isn't to say I don't like GFII as is because I do, I just prefer the DeNiro part far better.
Is very bad to steal Jobu's rum. Is very bad.

Agree 100%. I forget too.

Personally I thought Deniro channeled Brando's performance so well that its chilling. When I go through Deniros filmography in my head I seem to almost omit this performance on some subconcious level. Its like I totally forget that two actors portrayed Vito (one young one old). In fact when I think of Vito I dont think about Brando or Deniro at all.
Not too many characters have that impact on me. Maybe just the one.