tl;dr: It's almost identical to FFT, except it loads a lot faster and runs smoother. Good mechanics and class abilities. Cool spell effects. Weird art (but great battle maps). Fan-fic tier writing.

Full Review:
Fell Seal: Arbiter's Mark is Final Fantasy Tactics reincarnated. It's not enough to say that it's an homage or "of the same genre." It's identical to the original Final Fantasy Tactics in more ways than those words do justice to. The layout feels the same, the maps feel the same, the class system feels the same, the attacks feel the same, etc. There are some key differences, however. Most of those are evolutions of FFT's systems or aesthetic differences.

The mechanics are good. Items restock at the end of every battle, for one thing. Status effects seem to work better and can be implemented by ranged weapons via class skills, making some class archetypes that were weak in FFT feel strong in Fell Seal. One notable class skill is the humble tackle, which becomes far more useful and fun in Fell Seal, as it frequently does more damage than a base attack, depending on how it interacts with the map or even other characters. The classic cross-shape formation from FFT has a weakness now, in that it opens you up to free, heightened multi-target damage. The push effect is also guaranteed, meaning positioning on elevated terrain is far more important to consider.

One of the biggest flaws in Fell Seal so far is the Deviant Art level character writing and styling. Some of the scenarios and dialogue play out like they're lifted wholesale from a fan-fiction, and the expressions in the portraits are jarring, as the portraits themselves are very western in style and seem to be styled after paintings from the Baroque or Pre-Raphaelite movement, but the characters emote through alternate portraits which take that same Baroque style and apply anime expressions to it. The neutral portraits are good, but these anime-expression versions are not.

The backgrounds, on the other hand, are beautiful. They're hand-drawn and look better than FFT's maps (and I always liked FFT's maps). If there's one thing about this game's art that's really notable, it's the battlegrounds. The colors pop and their are lots of interesting little touches, and since the primacy of the game is fighting on these dressed-up grids, this is a big green flag for the game. You'll be spending a lot of time looking at the maps, so it's good that they're the best visuals the game has to offer.

The spell effects are also a highlight, and one of the elements of Fell Seal that surpasses FFT. Water I gives you icicles that stab your foes. When you get Water II, though, Instead of just slightly bigger icicles, you see ice swords that stab the target. Other spells have similarly interesting and thematically-appropriate effects.

The music is nice, but it hasn't really stood out to me so far. FFT's soundtrack is legendary. I'm only 12 hours into the game at this point, so maybe there are better tracks awaiting me.

I didn't like the main characters at first, but they're growing on me. You can still recruit generic characters like in FFT, and I have my team composed of 3 or 4 of those with 2 or 3 story characters most of the time. You can also change their appearances, outfits, and names at any time through the guild shops. This level of customization is a welcome addition. The portraits for generic characters are blander than FFT's, but the game also supports custom portraits, which is a nice perk.

If you liked Final Fantasy Tactics for the gameplay, Fell Seal: Arbiter's Mark is excellent. If you liked it for the aesthetic, it mostly misses the mark, but is not without some merits. If you liked it for both, I think you'll come out ahead with this game.