Like some of you I have also completed Ghost of Tsushima (base game, Iki Island, Legends MP), except for the new game + mode.
Honestly, this is one of my fav SIE games. Just a wonderful experience from beginning to end. It's not perfect, though. Textures could really use some work (though art style really makes up for it - a really gorgeous game to look at), the story is serviceable (though it has some incredible highs, like the final story mission), and there are limited enemies/ activities in the base game (remedied by Iki island expansion).
Iki Island does improve upon a few things from the main game: namely more enemy types (3 I believe), more wild animals (mainly the addition of monkeys), and new activities (animal sanctuaries, archery challenges). Iki Island also introduces hidden missions (i think there's 5) - they're usually quite small in nature, but they're different from the rumours you get in the base game. In the base game there are ppl you can talk to and they'll tell you about an incident, and this appears on the map. In Iki, you either need to randomly come across this mission when traversing, or you can listen in on conversations from NPCs to figure out their location.
But Iki is also glitchy. Nothing that braeks the game but random stuff like birds getting stuck mid flight, enemies disappearing upon death, their weapons randomly spinning in cutscenes. I think I encounterd 6 instances of this and they were more funny than anything else.
legends mode is a fantastic piece of MP. It also has it's own story divided into 2 parts: the story missions (which can be done with 1 other person) and the 3 raids (which require you to have a group of 4 and everyone to be max level). The raids are quite long but thankfully I matfched with 3 others who knew how to do the 2nd raid and finished it in 40 mins (though I had to read up what to do before hand because this raid takes ppl up to 4 hours apparently).
The MP is very meaty and a lot of fun.
Anyhows, GoT2 is probably my most anticipated SIE game now, alongside TloU3. I have thoughts on what I want to see but will wait for the reveal first.