You should definitely play 2 and 3 if you liked 1. As I stated in my write-up I liked 2 much better than 1 and some ways better than 3. But if you look at all 3 games as a whole they are very similar to each other. 2 definitely has the better story from the trilogy. 3 probably has the best gameplay but the storyline is kinda lolworthy really.
Dawn of Dreams is well... different from the first 3 games. Will you like the characters? I don't know. I personally like them quite a bit. Do they have cliche JRPG characteristics? And this is gonna disappoint you. Yes they do.
However character development and story isn't the main focus (Although the story is actually quite good and there is a fair amount of character development as well) just like the previous Onimusha game. The gameplay is also quite different from the previous entries because it has RPG elements like leveling up and the ability to equip a ton of weapons and equipments.
I'm gonna spoil the list a bit and tell you that 'Dawn of Dreams' IS on the list and as you can see it hasn't appeared yet. Which can only mean it is my favorite from the Onimusha series. So stick around a little longer and you'll see my take on what is probably my favorite underrated masterpiece.
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Rock n' Roll and Glam Metal... It never died