Well, since I've read several reviews that don't describe it satisfactorily, here we go:

Graphics: It's pixel art, before someone buys it they should watch some gameplay. If you don't like this type of graphics, then your eyes will get tired of this game.

Gameplay: Excellent, fast rogue-like game where progression comes through each death. If you don't know what a rogue-like game is, google it to have a clear idea of what to expect. Addictive action game without a dull moment.

Mobs/Bosses: Variety of enemies even in the basic version of the game, classic system where you have to memorize their moves in order to not find yourself in a difficult situation. The bosses are not difficult, except maybe the last one.

Builds: The game offers the possibility of 3 builds: brutality (melee), tactics (ranged), survival (tank). Each build offers a different experience, but all 3 are satisfying.

Difficulty: The game may seem difficult or even impossible at first, but with time and enough gameplay, it becomes easier. Upon completion, you are given an item as a reward, which if equipped, makes the game harder and so on (similar to ng+ and so on in the Souls games).

Similarity to Souls games: Absolutely none, it reminds more of metroidvania games, but without partial saves, etc. Dead Cells must be completed in one run.

Tldr: The game is a masterpiece. The feeling of rogue-like games where you have to reach the end in one run is truly addictive. Even if you finish it once, you can spend endless hours in subsequent runs to unlock several weapons in the game.

Dead Cells is a Rogue-like game.
Meaning it is a game where every time you lose, you start again from the beginning with the maps and enemies of the level changing, and every item you find is random. However, your efforts are not completely in vain, as in each run you find abilities and tricks to make the next ones easier. If you manage to reach the checkpoint, you can spend the cells you collected to improve the items you start with and unlock alternative routes that you can take.

Like all games of its genre, the game is theoretically short to reach from the beginning to the end. How fast you will do it depends on how quickly you get the right items at the right time, your upgrades will be enough, and everything will go well for you to reach and defeat the final boss. Like all recent rogue-likes, no run is the same, where each time you can find different items or even go to completely different areas and bosses, and even months later you will find items for the first time. From this perspective, the game is significantly long.

WARNING:
The "Action Game of the Year edition" of this game does not include any of the DLCs (not even the hated Voucher Codes). In the package, it includes a keychain, a mini artbook, and a double cover. The "DLC" mentioned on the packaging is, although large, the name of one of the free patches that are automatically downloaded and new ones are released until today. The only paid DLC of the game, "Bad Seed," is not included, and the version of the game on the disc is 1.0. The current version of the game is 1.17.

The game is a 2D roguelike which means increased difficulty (lack of checkpoints, loss of exp points upon death, etc.) which may discourage people who do not approach it with the right mindset. Dead Cells is based on the player's progress and not the character's. It is not an RPG where you can sit in an area grinding for hours to make the game easier. The action is fast-paced but also strategic, which you discover on your own by learning from mistakes.

However, there are permanent upgrades and even shortcuts that you can unlock for convenience. Obviously, these games are not for everyone as they are more difficult than usual, but it is by no means bad design as the challenge is the whole point. Just like it's not bad, for example, that driving in Gran Turismo is more difficult than driving in GTA.

Apart from its unique gameplay, Dead Cells has a wonderful art style and the quality/price ratio is fantastic compared to even more expensive sidescrollers like Mega Man 11. Overall, it requires patience if you are a beginner in this type of games. There is no easy mode or anything similar.