Ok I've played through Chapter 1, here is my initial take on Tainted Grail (no spoilers).
First and foremost, it's a very engrossing game. I really like the story elements, and I can't wait to play more to see how the game unfolds. People have said it's like a mix between Gloomhaven and 7th Continent, but it's much closer to the latter. In fact, I don't see very much similarity at all to Gloomhaven, other than combat is done with ability cards. Even then, it's not that similar because in GH you have all your cards in front of you to strategize, while in TG you start with 3 random cards out of a starting deck of 15, and then you draw one card per turn thereafter, so it's much more random.
Things I like about TG:
1. The story is very well developed, which is something that's always been a weak spot in GH. Not so here. I think the story is it's strongest point.
2. The contents of the game are all very good quality, gorgious production values throughout. If I had to say anything negative I would say I wish the cards were on heavier stock, but that's a minor quibble.
3. I haven't tried all the characters, but we are playing with 3 so far (Maggot, Ailei, and Arev). I am also doing a solo game with Beor (more on that later). I did get Niamh as part of my package, but none of us have tried her yet. All the characters are appealing to play, and they all play a part in the overarching story as you will see. I like how each of them has positive and negative attributes, it makes decision making more challenging.
Things I don't like about TG:
1. Downtime. There is a lot of it. This is not a fast-paced game in any sense. First, it suffers from the same fiddliness as 7C, which is you constantly need to get away from the game board to do something else. In 7C, you had to go back to the box to get new cards. In TG, you need to read from the exploration manual. Obviously on future playthroughs things will go quicker because you won't have to read everything again in such detail, but the pace is slow. Not necessarily a negative, but be aware of it. Frankly, it lends to a more roleplaying element as you become more invested in the story.
2. Analysis Paralysis. A real thing in this game, especially when it comes to combat and diplomacy. Let's start with the basics. Since you start with 3 cards, you can lay them down in 6 unique permutations. This only gets worse if you draw more cards. The issue is, there is optimal plays, and you have to find it. Which means you will spend a considerable amount of time laying the cards down in the different orders in order to try and find the best combination. That's only if you are the only active player. For every party member, they will bring their 3 cards as well, so now you are looking at an exponentially larger amount of possible combinations to go through. This should get better over time as everyone learns their cards, but you have 4 unique archetypes that have different cards....so yeah.
3. Alpha-gaming. I am most guilty of this in TG, which I never do usually, but let me explain. The only people involved in combat or diplomacy are the active characters, i.e. one of more people on the same tile. So what do you do if you are not involved? Good question. This goes back to downtime. If you aren't involved, then either watch your teammates muddle through the encounter, or break out your mobile phone, or I dunno. Since my partner isn't that experienced in gaming, she's having a harder time understanding how best to play her cards, so she asks for my help even when I'm not involved. I've been trying not to be intrusive, but sometimes she takes so long I will point out the optimal combo so we can move along.
As I mentioned earlier, I am also playing a solo game so I can go through the content faster, since my usual group only meets once a week and we still playing GH, so !'m not sure how much time we can devote to TG. That being said, I have a feeling that this game has the same pros/cons as 7C, which means it will play better as lower player counts. This game definitely plays faster as solo, since there is no need to read out loud, and there is no downtime between player turns. As of now I would rate this game something like 7/10, and probably 8.5/10 for solo.