I'm unsure if this is actually an immersive sim (I feel like it is very game-y at times which would contradict it being an immersive sim). However, it is a very good game in my opinion. I have 100+ hours played in this game and I don't remember most of 'em, it's a very replayable game.
This is the best single-player game ever made in the past 15 years, in my opinion. It abandons nearly all fantasy elements (with the exception of some unrealistic potions and witchcraft-y side mission(s)) with a focus on realism and historical accuracy. I'm not a history buff or a huge fan of the time period of which the game is set in (circa 1400AD) but I still appreciated it. Combat is kinda ass against multiple enemies and is super easy to cheese when you learn master strikes but is still enjoyable and requires skill to master. Hardcore mode makes exploring so much more enjoyable, it has the best forests I've ever seen in a game and it is a blast to get lost and doing things like looking for landmarks and using the Sun to identify directions. It will take you 5x as long to beat the game on hardcore but it's so wonderful. Play it if you can.
One of my favorite games. This game was clearly made with immersion and believability in mind when designing the mechanics and world. As far as I know, there haven't been any open world crime games that have gotten close to this game in that regard. Sue me but I like the gun-play. The harsh recoil on the Tommy-Gun makes it feel very powerful along with the other firearms in the game. I also like how your bullets don't just spawn on the crosshair but actually come out of the barrel of your gun, which is why you often get bullets hitting a surface that is close to you rather than where your crosshair is pointing.
In my opinion, this is the best immersive sim ever made. I'm not gonna be some weird anarcho-whateverist and pretend that this game is a "redpill" like others do, but the story is pretty good. (Is your entire world philosophy based off of a fictional video game story? Yikes). There are a lot of hidden areas and opportunities that are in the levels with incredibly non-linear level design. Good game, I don't recommend playing GMDX or Deus Ex: Revision as those change too much and ruin some parts of the game.
If there were AAA games in the first person parkour genre that weren't part of the Mirror's Edge series, Mirror's Edge would be slated as a mediocre, short, game. I don't think it's bad but holy cow, the combat sure is. Same with many levels in the game. Who would've thought that having huge parts of the game just essentially being quicktime events would be unfun?!?!