I haven't watched the Age of Resistance series, so I can't comment on that at all. What I can say is reading around, this game is basically a retelling of the TV series, though it does feel like a lot is missing. If you are looking at this game purely as an expansion of the lore of the original Dark Crystal movie, you may be better off watching the series with how much it feels like this version kind of jumps around.
That puts this game in an interesting position though, because it's never going to be a game you go into for the story. The likely more complete version is on Netflix, and it only really appeals to people who have seen the original Dark Crystal, so from a narrative point discussing this game feels entirely pointless. The only real thing I can say is it feels choppy like a lot is missing, and it's only even worth diving into if you've seen the original movie, and that gives the game a pretty small audience overall.
I will say there are some interesting aspects to the lore, but nothing that pulls you in. Getting a chance to see how life was before the movie began was fairly interesting, even if we all know how it has to end up. Nothing seems like it flies in the face of the movie, at least not that I remember seeing, so it's not going to tarnish any childhood memories. I don't think it does anything all that fantastic, but nothing wrong either.
When discussing the gameplay, however, I am a bit torn. For a twenty dollar game, you have a fair bit of options. The Gelflings you can recruit and play as can level up in multiple job classes, and you may equip three abilities from the job you are currently using and any two you have learned from a secondary job. You build towards a tier three-class by leveling lower-tier jobs, and you seem to have a fair amount of ways to build your characters, even having two guys of the same class can see a lot of different results. It is everything you'd want out of a lower-cost strategy RPG.
Where the problems start to come in is relatively uninspired map designs and a lot of repeated enemy encounters. The game moves at a pretty slow pace, and unless you take a fair bit of time grinding you'll find yourself having to do the same moves over and over as you don't get a lot of options early on. While the mechanics of the game themselves are well done, and the ideas are all solid, these issues tend to make the game feel like it drags on a lot longer than it should. It's an overall poor execution.
It's also a bit odd that the game sometimes slows noticeably in frame rate despite not being that high end in terms of graphics, at least on the Switch version, and there are some odd issues with the menus where you'll scroll down and it will suddenly jump beneath the skill you have highlighted. These aren't big issues since they are easily worked around and don't impact things too much, but it does feel like it's slowing down an already slow feeling game as a result.
This game has a lot of good things going for it, but nothing great enough to compensate for the negative. It's not an especially bad way to spend twenty dollars if nothing else seems interesting to you at the time, but nothing to go out of your way to play unless you really can't find anything else worthwhile and find yourself in need of playing a new game.