What are some established game series that you haven't played yet but plan to try sometime in the future? The only rule is that it has to be a series with multiple entries and not just a single game. Why do you think you will like them. How do you plan to jump in?

For me:

Devil May Cry - I like similar games such as God of War and Bayonetta. The first four games are available on PS Now so that's where I'll play them.

The World Ends With You - I liked Kingdom Hearts. I'm trying to play more JRPGs in general. I got the Final Mix edition on Switch. If I like it I will play the sequel.

What about you?

Tales
The World Ends With You
Bayonetta
Battlefield
Code: Realize
BioShock

Ghost of Tsushima - Was super hypes for it, but I got caught up playing other games when it released. Now I got it on PS5, and I am caught up with getting the plat in Demon Souls and SMTV on Switch. Probably play Ratchet and Clank next because I want to play Forbidden West and Eldin Ring, and I want to avoid open world overload.

Days Gone - See above...but less hyped when it launched.

Halo 1-5 - I am new to the Halo fandom, Infinite being my first SP experience. I now want to visit the old games because it blew me away and I really want to get into the lore of the franchise.

Pretty much all the niche JRPG series that would take too much time, but would definitely be enjoyable games.

Examples include:

Tales
Legend of Heroes
Atelier

SMT, but I play Persona

Metal Gear and Shin Megami Tensei

JRPG as a genre. I grew up on western RPGs, shooters, and the occasional platformer, but really sinking my teeth into a JRPG is something I still haven’t don’t, somehow.

Another one is the Soulsborne genre.

Glad you liked Halo! If you are new to the series it can be tempting to want and try to play them in story order (Reach, CE, 2, ODST, 3, 4, 5), but I would recommend playing them in the order they were released instead (CE, 2, 3, ODST, Reach, 4, 5). The games evolve a lot mechanically over each title and they kind of assumed you had already played the one that came before it in a lot of cases. 

Fire Emblem - I'm a big fan of tactical RPGs, but I've never gotten around to Fire Emblem. I finally bought Three Houses for last Christmas. Just haven't started it yet.
Divinity: Original Sin - Just need to find the time for it somewhere.
Bioshock

System Shock - Not got around to playing the games when they first released. The remake looks interesting though.
Nioh - Have 1+2 for PS4. Haven't started playing it properly (was in tutorial stages) then dropped. Will pick up again at some point.
Bayonetta - Have the first game on PS3 and PC. Sitting on it for some reason.
Just Cause - Been meaning to try this though never got around to it.

Ys.