I played GoW 1 through 3 plus GoW 2018 and Ragnarok back to back not too long ago. This was my first time playing each game. My thoughts:
GoW 1 is alright. It's a bit too button-mashy for my liking, and I wish it had more weapon variety. It's not a bad game, but it's definitely a product of its time.
GoW 2 is probably my favourite of the OG trilogy. It's just a fun game to blast through, and it fixed all of the issues I had with the first game. I don't have much else to say about it - it's just a great game.
GoW 3 is my second favourite of the OG trilogy. It's basically a nicer looking GoW 2 with a much larger scope. That said, I didn't like the weapon selection as much. There are also parts of the game that were trying to be more cinematic, like the diving sections, which I thought were just okay. Some of the puzzles were cool though, like the perspective puzzle with the stairs. They tried to humanize Kratos by making him care about Pandora's wellbeing, and that just fell completely flat for me. Still a great game though.
I loved GoW 2018, to the point where it might be my favourite in the series. I think the game is fantastic at integrating the gameplay together with the story in a way that creates a strong emotional resonance with the player. It's also much better at humanizing Kratos than what GoW 3 tried to do with Pandora, in my opinion. It helps that this game was a very personal story that felt isolated from everything else, with the Norse mythology stuff acting as a nice backdrop. The combat is incredibly fluid, and the puzzles are fun to figure out. It also has so many little details that really add up, like how characters naturally end conversations when you get off the boat on the overworld. It really feels like the devs put a lot of time and care into the game.
GoW Ragnarok was just okay. Gameplay-wise it didn't feel like much of an improvement over the previous game. It just made some aspects of the game grindier, which I'm not the biggest fan of. Story-wise they pretty much did the opposite of what GoW 2018 did: Instead of a personal story between Kratos and Atreus with the Norse elements in the background, now we get a grand epic story about the Norse stuff with Kratos and Atreus feeling more like side characters. Actually, let me put it this way: GoW 2018 is a story about Kratos and Atreus. GoW Ragnarok is a story about everyone else. You do get some great character moments as a result, which I did enjoy, and then it just.... ends. This game didn't have as big of an emotional impact on me as the previous one did. AND FUCK IRONWOOD WHAT A WASTE OF TIME THAT SECTION IS sorry I lost my composure there for a second.
I haven't played Ascension or the PSP games, but from what I've played you can't really go wrong with any of these games.