In this post I will answer the questions you have here, on the game page, and one from the Discord server.
What are the 4 key gameplay elements in Anachronium?
I'm having a hard time breaking things down into 4 points. The core is strategy. First strategy in picking the cards you will have for the upcoming combat, based on what you think, or know, may be there. There is an intriguing story to the game, and I enjoy following it, but I'm not sure it is a "gameplay element" as you, so far, don't influence it, and you could play the game with no story, such as for replaying, and it would still be a fun game. After selecting your cards, you then have to decide how best to use them in combat. Your first time facing a new combat you need to analyze the enemies and form an initial plan based on what you know or think about them. As they show you new behavior you may need to adjust. There are many cards and many ways to use them, so picking and how you use the cards would be the top 2 key gameplay elements. If you add more to use the credits on, then balancing the use of your credits could become an important element as well. In the end I keep coming back to strategy being the key, and anything else is just a part of the overall strategy of the game. Maybe I'm just not in the right mindset right now to break things down into finer elements that this is probably meaning.
Is the game generally fun?
Yes. I've played through the game several times now, and enjoy playing each time.
What cards seemed the most appealing to play?
Lasers are essential for some fights with shields. I personally liked the Laser of Lament and Phantom Ray, as well as the Remorse Flower and Phantom Flower, though the cost of 5 meant that I didn't really get to use the Phantom Flower.
Which cards seemed pointless for your experience?
Self Destruct. I see no reason to use it over any other damage dealing option. It is the kind of thing that I would only use as a last resort, and with only 4 card slots there is no way I'd waste one on it. If it was like the basic attack and always available, then I might find a situation where it would be the best choice.
How difficult is the game?
I find the game to be quite easy. I have not lost any ships, and in this playthrough I only once had 1 ship get down to 1 HP, right before I ended the fight.
How engaging is the story? At what point were you hooked(if at all)?
I like the story. It has real world comparisons and feels genuine. I am looking forward to seeing the rest of it. I can't say I was hooked at a certain point, as I don't recall my first playthrough.
Did you complete the game? If not what was the major reason?
Yes.
Does the game feel replayable? Or more of a one and done experience?
I think there is some replay value in trying out different cards, but there needs to be an option to skip all the story for those who just want to try to get a better score on a level, or want to try different cards. I was not able to skip the in combat story with E, so adding support for that would be a start. But I think it would be good to have a mode or setting somewhere, possibly unlocked after beating the game, that allows auto skipping all dialogue and cinematics for replays.
Another thing that would help with replay would be some randomness to the enemies you face, or even a procedurally generated mode. There is significantly more challenge when you are going into the next combat blind about what you will face and have to pick your cards. There can be fun in trying to do better on a known fight, but I think it has a limit and an option for random fights would help. This could be a Battle Arena that you unlock after beating the main game where you can select the difficulty and how many fights there will be, and it will be randomly generated from that.
Balance of the cards.
I didn't really test out a lot of cards this time. I think they have a decent balance currently. There are many different ways to play, partly based on the player's skill. I used a somewhat different set of cards early on this time due to the better balancing of the Blast Gun. There are many I have not tried yet, so can't judge.