It's another reason why I'm not as big a fan of 0 as the majority of the Western world is; it changed a fair amount of things around that were established by the previous 5 games in the series, namely (in this case) Majima and Kiryu's relationship (which also saw unnecessary changes in Kiwami).
Majima always had an attitude towards Kiryu of honour, however they were never friends or even companions; they simply were two guys on even levels of the Tojo Clan Hierarchy, when Majima got boosted to family head while Kiryu was in prison.
He is a boss, an antagonist (hence the reasoning behind why you fought him in the first two games) and only softened his attitude towards Kiryu, AFTER he ascended as the 4th. 2/Kiwami 2 is when Majima started to mellow-out a bit towards Kiryu and at that point, they became buddies, but before then, they were merely enemies who had a deep respect for each other and their past included infrequent encounters.
Then 0 happens and all of a sudden, due to one ******* scene, he's shoehorned as a companion to Kiryu, a long-lost friend; that last scene of the game was enjoyable as a fan, but it was so out of place, as they don't even know each other at that point in their lives.
Because of fanservice, Majima Anywhere happens (to death) and is completely out of place with the tone of the rest of the game; the Shimano family (of which Majima is a Captain) and the Dojima/Kazama families are rivals and do not get along, which is why Majima is much more antagonistic and sadistic towards Kiryu in 1/Kiwami and at first in 2/Kiwami 2.
The events at the beginning of 3 start to show a softer side of Majima, but 0 is a prequel and it completely negates that established character from earlier in the series.
Kiryu is also no punk; he's a loyal and fierce companion/brother to Nishkiyama and the rest of the game will show you how and (more importantly) WHEN Nishkiyama flipped the switched and turned into an antagonist... 1's plot is done so well and intelligently, probably due to the fact that it is the only plot of the game where Nagoshi was in charge of everything, save for the physical writing and putting together of ideas (which Seishu did, after he was brought on).
Anyways, a lot of mechanics may not be as smooth as other games in the series, but that's plainly due to the fact that the game was updated/remade basically 1:1, with graphical updates and an expansion of the fighting styles (and an updated soundtrack, which is arguably worse though still far from bad), but leaving everything else intact. Still, have fun with it and enjoy the excellent plot!
TL;DR 0 retconned a bunch of things and it didn't need to, hence why you see the difference.