I have a long post below talking about card balance and strategy.
I will write a long post here about the systems / design of the game.
Prospect:
The most consistent strategy I've found so far (see my long post below) is to rely heavily on Prospect, buy useful cantrips like Ingot or Lens, buy a very small number of enabler cards like Amber(s) or The Creature and nothing else.
Unless I'm trying to make a build work just for the fun of experimentation I am ignoring the vast majority of non-cantrip cards as well as the expensive minerals.
I think starting with Prospect in the deck pushes me in this direction.
If my 10th special card were randomized from a special pool of unique starter cards (or maybe I get to pick 1 of 3 which are drawn from a larger random pool), it would be fine for Prospect to power a very consistent strategy, because I wouldn't always get the Prospect to use.
I think it would be more interesting if my special starter card has different synergies depending on which one I get and which pushes me in different directions in terms of shopping and how I play my turns right from the start.
If I get Prospect every run it has to be powerful enough to really make a difference, but this risks it becoming the entire focal point of the game.
If I don't get it every run it's fine to warp certain runs around it because I have plenty of other runs that are about other things.
Re-rolls:
I didn't even see the re-roll shop button for the first few runs.
I think it should be a large icon in the row with the cards.
Even after I saw it, I almost never use it because it's just too expensive.
I think it should have a fixed and mounting cost within each shop visit (maybe 5 -> 10 -> 15 etc) so that it's tempting to re-roll a bit but you might not find anything and it's expensive to re-roll a lot digging for particular cards.
It's also nice if I get to feel rich later in the game when I am rich.
If you scale up the costs of almost *everything* I never get to really feel rich.
Maybe the cards scale up more in cost than they do at present but the re-roll stays cheap. (edit: as depth increases)
The high cost of re-rolling contributes to my "no synergy" Prospect approach, since I know it's very risky to take cards early on that will require specific synergy later.
If I post a victory screenshot and it shows re-rolls it's usually because I was about to start The Core and there's no more reason to save Ore, so I might as well roll for Helmet, Scorium Geode, etc.
Shop presentation:
I really like the way that the shop gives 1 random Ore and 1 random Scorium.
I apologize if this is already the case & I just didn't realize, but I think it would be nice if the shop had "slots" for Tool and Action plus a wild slot that could be anything.
If certain cards are really unique or powerful maybe they only show up in that wild slot so they don't appear too often.
(Edit: Also if re-rolls are cheaper you don't need to give so many slots of Shop).
Utilities:
The utilities all scale up in cost.
For Hourglass as you get more Hourglasses probably there's some diminishing returns, but it's such a powerful effect and I get so few that I don't think this is a problem at all.
I think 350->999 is pretty steep and it's more interesting at like 500.
If you just want it to max out at 350 then just don't give me the option to buy it again at all. (edit: maybe it says SOLD OUT instead of a price)
Showing Hourglass at 999 when that's not intended to really be an option is kind of spiteful.
For Dynamite it's not a super powerful effect but the value scales up as you get more (first you eliminate 10% of your chaff, then 11.1% then 12.5% etc)
For Hammer, though, the value scales down (the buff is a smaller and smaller proportion of the value of the deck; initially I have 3 energy twice on 5-point cards so 30 points and the 3-point Hammer is 10%; quickly this reduces to negligible).
In most builds I could play, I'm taking the 15-cost Hammer on my best Ore for early economy, then I'm only ever touching Hammer again if I'm rich or I really need to buff a particular card.
I think it would be more interesting if Hammer was at a fixed cost (maybe 20) and its declining usefulness came from the fact that it's a smaller and smaller % contribution to the deck's power.
A fixed-cost Hammer would also reduce the reliance on Prospect for upgrading cards.
(Edit: also you might consider allowing multiple Hammer uses in a single shop visit similar to what I'm proposing for re-rolls, either at a fixed cost or an increasing cost within that 1 visit, ie 20->30->40 but then if you come visit the shop at the next Depth it's 20 again).
UI
Maybe I'm just dumb, but it took me a lot of runs to understand the Depth and Hourglass icons.
I was surprised for a while that I kept getting extra turns until I figured out that 0 counts as a turn, so the hourglass icon on the HUD is how many extra turns you have not counting the current turn (rather than how many total turns you have counting the current one). This might just be my fault - you have to do it one way or the other and either can be interpreted wrongly.
When shopping it wasn't always clear to me what depth I'm about to start.
Unless I'm mistaken I think it shows the depth of the level I just beat rather than the one I'm about to start, so when a run was going really smoothly and I wasn't thinking about depth sometimes I was surprised to start The Core.
We also go from fight to shopping without seeing the world map (which saves a screen compared to doing map both before and after).
I think if the a certain depth is map -> shop -> fight I get all the relevant information when I need it in the same number of screens as current at the cost of the flavor hit of separating the map and the expedition.
I would much rather be told to prepare for a certain flavor of level with a certain score goal then do my shopping.
Maybe I can check the map from the shop screen?
(Edit: maybe the go-to-fight button has the difficulty icon from the map screen?)
I think the Hourglass icon and Depth icon are kind of in conflict (assuming I've remembered and interpreted them correctly). The turn counter shows how many future turns I have, while the depth counter shows my previous depth.
Edited to add:
Another thing - I think it would be cool to track "overkill" on level score so I can see that I did 250/225 or whatever.
Even if this isn't tied to any reward in the game, it feels good to see how powerful my Scorium is getting.
Right now my major power fantasy reward is from making lots of Ore but not really from making lots of Scorium.
"Woah, I've got 500 Ore to spend, that's crazy" feels really good.
"Woah my Huge Scorium beat that level in only 3 turns" feels good but there's not a lot of gradation of experience, especially once you get good at the game and something like that is a routine event.
It's also helpful to the player to know exactly how strong he is, but that's quite secondary IMO; the player needs to be challenged so not everything that helps him is the right design.