The strong points of A Plague Tale: Innocence are its visuals, atmosphere, and story. The deadliness of the plague, the destruction it wreaks upon the land and the people, as well as the cruelty of the war and the Inquisition are depicted vividly throughout the game.
In terms of gameplay, the game combines several elements including action, survival, puzzle, and stealth. However, you should not expect the game to excel at any of these.
In the majority of cases, the action part of the game only involves using Amicia's sling to kill Inquisition soldiers. There isn't any fancy move or secret technique to be learned. Simply aim the sling at a soldier's head and hit the button - a simple task, given the aim-assist function that is always there. Amicia is no action heroine. While she can dodge, this move only really works against a few certain soldiers in the game. Most other soldiers will close in very quickly and instantly kill Amicia once they catch up to her. There is no kiting or outrunning these enemies either, unless you have Amicia continuously run around obstacles.
As for stealth, the basic mechanics are there: crouching behind covers and distracting enemies with rocks or breakable pots. This is no stealth game, however. There are no various techniques to silently take down enemies for you to learn. There is no hiding bodies, either - which is to be expected, as Amicia is just a kid. If there is a "stealth route" through a group of soldiers, which is intended for Amicia to take, it is also quite obvious.
There is a bit of a survival element, since it is usually easy for Amicia to die if she is detected, and also there are resources to manage. Resources should not be much of a concern, however, as the game provides Amicia with an ample amount of them. Prior to any section that specifically requires certain types of resources, these resources are always provided by the game, conveniently lying around for Amicia to pick up.
Puzzles in the game in most cases involve playing around with light sources to get through rat swarms. Some puzzles require team work from Amicia and other characters who are tagging along. In general, puzzles are simple, and you can tell at a glance what you are supposed to do. After a while, you start to get the feeling that half of the problems in the world can be solved with a sling and a handful of rocks.
In short, A Plague Tale does not try to be "hardcore" or exceedingly hard when it comes to any of its gameplay elements. Despite the fact that Amicia is just a kid armed with only a sling and a few rocks, killing enemy soldiers in the majority of cases is very easy, since it takes only a single shot. You can't really get lost exploring, as there is always only one route to take. The game is also fairly forgiving, as far as stealth and dealing with enemy soldiers are concerned. Soldier AI can be questionable at times, especially when the situation gets just a bit more complicated than "throwing a rock to create distraction". While chasing after Amicia, an enemy soldier may get so close to a swarm of rats that he has no time to run away before being swarmed, even though he should be able to clearly see that swarm from a hundred feet away. AI hiccups tend to crop up more often when Amicia is having a companion (not Hugo) tagging along. An enemy soldier may have trouble noticing the companion even though they are crouching right in front of him. Of course, given the fact that you cannot control the companion, and they usually don't do an excellent job at staying behind covers when following Amicia around, it is a good thing that the game is forgiving.
There are other details that you may also want to ignore, in order to better enjoy the game. A chain is holding an entire metal cage, with an adult in it, suspended in the air, yet you can break said chain by slinging a rock at it. Many chains in the game can be broken this way. If they are so easily broken, they probably should have broken long before that point. When a five-year-old kid manages to sneak through an entire cathedral full of soldiers and priests, to get all the way down into the prison, or when Amicia kills a group of archers at about 80 feet away, each with a single headshot from the sling, you can't help but feel it is a bit too much. There are some other story events which you may find "questionable", depending on how you look at them. In the end, the game does not quite explain how exactly so many rats can just disappear completely in just a couple days, or what exactly causes them to do so.
Again, the main emphasis of the game is in the struggle of Amicia and Hugo and other kids against an extremely hostile environment and impossible odds. How Amicia and Hugo suddenly lose everything, how quickly everything descends into chaos, how they become fast friends with other kids, how they try to be there for one another and help one another through hardship - all these details make you feel sympathy towards them, hope that they will be alright, and wonder what will happen next. This is a really good game when you just want to enjoy a compelling story without having to struggle with the gameplay.