just finished it and I loved it. like it was mentioned, the end was kind of a meh but I think its because yuno wasnt quite herself in the last few chapters. as you read more and more you get to know her as a psycho yandere in love with yukki who would do literaly anything to be with him but in the end her personnality suddenly changes and she doesnt love him anymore and she wants to kill him. that kinda put me off. I dont really mind the fact that her memories were kept and inserted into the third yuno as I prefer that ending to other possibilities.
But there is a way for the 1st yuno to with the second yukki (or first yukki with second yuno). if yuno went back in time and instead of killing herself would of have just watched her from the shadows untill the point when only yukki and yuno would remain, then killed her, with no one aware of her being there, yukki would of have been recognised as the last remaining diary holder and become god. at this point it is safe for yuno to come out of hiding since yukki is already a god and they can be together as two gods. and since she didnt kill the second yuno, the timeline would be the same as the first world, up until the point where one of them dies. so it would be basicly being with the original person.