Escape Simulator is a straightforward proposition that is basically what you would expect from a game like this.

It looks fine, with a flat shaded graphical style that works for what this game is trying to be and lends itself to the readability the game requires. The character models are fine, but not super appealing.

The actual gameplay is straightforward, picking up and manipulating objects to find your way out of a room full of puzzles. The rooms themselves are very small, unfortunately, which limits how much of surprise or interest can happen.
The interface can be finicky sometimes, with a bit of complication in picking up, interacting with, and disposing of items.
The puzzles are cute but not mind-blowing. Most of the fun comes from working with your friends to figure things out. There are also some opportunities to work on things in parallel, which is very satisfying and feels the most like a real escape room. A couple of the puzzles have obtuse or strange solutions, but the hint mechanic helped us work through the ones that felt unfair.

Not a bad way to spend a couple of hours with some friends solving simple puzzles and hanging out. I liked playing this in a group, but it would definitely be pretty boring in solo play (which isn't that surprising).
I would definitely have liked it more if the rooms themselves were a bit more interesting and some of the puzzles and UX had a usability pass done on them.

This DLC solves almost all the problems I have with the base game. It honestly shocked me how much better this works, especially considering how focused it is on the most purposely trite and annoying character in the Marvel Universe.
This is short, just consisting of a few missions, but it adds in a new enemy type, some new arenas, and Deadpool as a playable character.

Deadpool is written like a snarky jackass (just like everyone else in the game), but it works so much better in this context partly because that is who Deadpool is anyway and because Nolan North absolutely kills it as the voice.
Additionally, because everyone in Marvel knows Deadpool is annoying, they react to him believably, treating him like the fool he is. Blade's exasperation and Captain Marvel's begrudging acceptance but willingness to help out bring more to those characters than almost anything else in the main game. Even The Hunter's reaction of being completely down to hang out with Deadpool despite how obviously awful he is works as a much needed comedic beat at the Hunter's expense.
It throws into contrast how unbelievably everyone responds to everyone else in the game, who have similar levels of one note, insufferable character traits, but elicit no realistic reactions from the rest of the cast. Why would anyone ever even talk to the Tony Stark or Magik in this game?

Deadpool somehow looks better and is better animated than anyone else in the game. I don't understand this at all. It can't just be the facial modeling/animation budget, can it?

The structure of this DLC is how the whole game should have been. Deadpool arrives with a problem and you help him out with it over the course of a couple of missions by using whatever heroes you want. It wraps up with a cliffhanger and Deadpool hangs around to help in other missions.
All the interactions are centered on him, so other characters can just be themselves, rather than justifying how important they are in every single scene and line.
The relationship building makes more sense because there is no time pressure, it is just something you are doing mostly after you help him solve his vampire problem.

If the rest of the DLC is like this, I am definitely looking forward to it. Hopefully it does well enough that they can turn this into a platform for this kind of storytelling and leave the Midnight Suns as a vestigial part you can ignore and still get a whole experience.

This is a hard one for me to rate.

I like the tactical combat in Midnight Suns quite a bit. It is like a weird hybrid of Slay the Spire and, strangely, Into the Breach, but in 3d with super heroes.
You pick three heroes, impacting which cards will come up in your deck. There is some interesting puzzle-esque gameplay around kill order (certain moves are free if used to kill, certain enemies only have one hitpoint, you have other resources and options at your disposal to change the battlefield, etc...), and each of the heroes has fairly unique gameplay that is enabled by their cards or passive abilities.
As in Into the Breach, each fight takes place on a very small battlefield with reinforcements arriving every round. The number of abilities and cards that move units around also means you are constantly thinking about your positioning, the enemies positioning, and how you can exploit it.
The loop isn't quite as tight as Into the Breach or Slay the Spire, however. Actions can often have somewhat unpredictable results and movement is severely limited, except for every ability automatically moves you, so it is a hard resource to actually manage.
Despite that, it all adds up to an easy to pick up, satisfying little tactical experience with a lot of variety and a lot of flash.

Everything else about the game I really disliked.

Visually, this game is very rough. Character models are weird and low poly, textures take forever to load in and don't look that good, animations are stiff, boring, or just weird, and many of the visual effects don't know if they want to be super realistic or ripped directly from a comic book.

Beyond the tactical gameplay, Midnight Suns cribs from Persona, giving you sort of a day/night cycle you can use to get to know your fellow heroes, spending time with them and giving them gifts to increase their friendship levels for bonuses. This could be a cool idea (but see below about the dialog) if it were a bit more open in its implementation. There are specific, preset groups you join (a book club, a magic club, etc...) whose meetings are at set points over the course of the narrative. You are also given very few opportunities to actually pick who you will focus on (I specifically chose a hangout partner maybe 3-4 times through my entire playthrough). This makes the whole system feel like a pastiche, rather than specific events you are opting into, as in a Persona game.

The narrative in Midnight Suns is, at best, just really boring but usually really juvenile and silly. There isn't much driving things forward beyond a non-specific prophecy and an antagonist with unclear motivations. The characters engage in a lot of CW-style manufactured conflict and drama for reasons that are uninteresting or nonsensical. The game tries to create tension between the old school heroes (The Avengers) and the new school heroes (the Midnight Suns), but it just feels like schoolyard bullshit coming from people who are supposed to be competent adults. The characters are too busy one-upping each other or infighting to ever make me happy any of them are there.
They purposely throw agency and control over the team to the player avatar (why the most famous heroes in the world worship The Hunter is unexplained), but you are never actually given any agency to solve their squabbling or even take meaningful steps to advance your cause. You just end up waiting for the cutscenes that move the plot forward to happen.
The writing is similarly hard to deal with. Every character has one very obvious character trait and everything they say is just about that. Spider-man was bitten by a radioactive spider, Iron Man is a CEO, Ghost Rider has a vengeance demon inside him, etc... If these were small characters without much screentime, it would be fine, but this is hours and hours of dialog that just ends up being repetitive and uninteresting. It honestly feels like comic book writing from before comics writers realized they could make their characters have depth.
Additionally, every single line of dialog is some sort of snarky joke, usually related to that character's one identifiable trait. It is like every single character in every single scene is trying to steal the spotlight with every line they deliver. It makes every interaction trite and annoying in the extreme, especially because of the sheer amount of dialog that exists in the game.

This game has a glimmer of something really fun with the combat and even the basic structure of things, but it is just expressed in the wrong places. If they were less worried about The Hunter and the Midnight Suns, and just let you have fun vignettes with these heroes, solving problems on a smaller scale or in a shorter timeframe things would be more compelling, characters wouldn't be fighting for the spotlight, and the laid-back nature of things in the hub world would make much more sense.
The Deadpool DLC does exactly this and works much better and, if taken by itself, solves most of the problems I have with the game.

In the end, I like the tactical gameplay enough that I didn't completely dislike this game, but if you play it, be prepared to skip literally all of the dialog.