It's uncommon but can happen. A series can begin with some games that are just eh to bad then suddenly become pretty good.

Nier is a really interesting example. Nier is a spinoff of the PS2 Drakengard games. Those games are fucking awful. Interesting ideas but they play like garbage. Nier on PS3 and 360. Had brilliant music and story. Full of great ideas but the gameplay was very average. Then we come to Nier Automata. Brilliant story and writing. Same fantastic music. It also plays really well. Now it was not intended to be a full-on PG over the top combat. They intended to tone it down and it fits the game. I also believe it has the best dodge in any action-based combat. NA is easily one of the best games of this generation.

Killer Instinct. The older games have not aged well at all compared to the reboot. Even when it was new they were niche. The first games were more known for the unique he characters then fighting mechanic depth. 

Killzone to Killzone 2/3

SERIES, not game. SERIES.

Oopsie. Changed my post. 

Red Dead Revolver was a competent, but not especially memorable shooting game. Red Dead Redemption was the stuff of legend.

I find this with a lot of fighters, as technology has improved so have the gameplay as it's become smoother and the gameplays are more streamlined because the characters are no longer 5 pixels or 10 polygons :P MK and SF both went through a lull during 6th gen and came back stronger in 7th and 8th.

I think Nier is way better than Automata.

But I do agree that Drakengard is trash and seeing Nier spawn from that was interesting.

Mario Sunshine to Mario Galaxy; from a game was practically the definition of "meh" to one of the greatest video games ever created.

100% agree on Nier. Automata is just so perfect. 

100% disagree on Killer Instinct. 

Might be a weird pick but i'd say God of War. I do consider I & II to be mediocre. III was really good and God of War for Ps4 was fantastic. 

To a lesser extent, Castlevania. After the fantastic SOTN every single Castlevania was either bad or okayish and we got a bunch of SOTN imitations for portable console. I cant Stand Soma Cruz games myself. But then came Lord of Shadows and it was just fantastic, loved it, it was enganging and fun, even if it wasnt particularly original. Sadly that all went to shit with the sequel.