Never played Nioh 1. Analysis told me I can go right ahead and just play Nioh 2(no regrets!) which is Nioh 1 but better in every way and has a more complex combat system with itemization on par with Diablo 2. Some dislike this because they have to use brain to figure out what gear is good but to me it's more engaging this way.
Wo Long is a different beast from Nioh 2 and thus wants you to play a different way. And is a more streamlined experience to an extent.
Rise of the Ronin is what I've read is Nioh 1 + Wo Long and Open World....but I think it turns out it's Tenchu: Nioh Edition.
I've yet to play RotR to judge properly but it's probably an easier Nioh 2 from a mechanics standpoint.
Nioh 2 has a great in-depth system where the player and enemies/bosses use the same rules in combat. Anything they can do to pressure you...you can do to them. And among that you can Megaman Core Souls for abilities and passives, turn into one of 3 interchangeable Demons, stance swap for different attacks/movesets, timed button presses for quick Ki Pulse regeneration, red telegraphed attacks that must be avoided or interrupted or suffer heavy damage, mix and match consumables, ranged weapons, magic and your skills level up the more you use those skills. Use Ninjutsu you get skill points for Ninjutsu. Stellar. Not to mention the build variety.
And just when you get the hang of it you fight a boss that becomes a roadblock and teaches you new mechanics and makes you a better player. To a point where you memorize how every enemy fights and can make decisions on how to engage them. And after learning the fight...that tough enemy or boss becomes a walk in the park.
So let's frame it as Nioh 1 was the beginning, Nioh 2 is Peak, Wo Long is more streamlined and RotR is supposed to be a healthy mix of Nioh and Wo Long.
I think from a Lore standpoint Nioh 2 should be tougher since you are fighting Demons and Yokai primarily. Wo Long and RotR not as much. Not sure RotR has any.
