Clearly wearing its vampire survivors inspiration on its sleeve, it's a little tricky to fairly review Army of Ruin, a new auto shooter which will end in slightly less absurd levels of bullet hell and screen confetti than its predecessor.
It's even more impossible to review without comparison, partly because VS did it so well. So, compared to VS, there are far, far more weapons and trinkets (what vs calls passive weapons), and the meta progression is a little slower. You'll need to use your coins to unlock extra weapon and trinket slots, along with the usual damage, fire rate, size, etc.
One upgrade I desperately missed from VS is armor, which generally falls off quickly but can make the beginning of difficult stages a lot smoother. Many, many runs on high difficulty died in the first 3 minutes as I simply could not get the progression I needed to survive.
The difficulty here will remain high compared to VS (unless you were buying curse levels there), especially as you unlock ruin levels. Ruin is like a small extra modifier, maybe there's an extra wave of cannon fodder periodically and you earn 10% less XP, or the bosses have a poison aura or something.
Unlocking after the early game will mostly require you to do specific things like "beat stage x at ruin y with character z".. the most extreme versions I've seen also require 2 specific items to be acquired. Each challenge will lead to another weapon, character, trinket, and then more challenges based on that unlock. As of this review, I have somewhere between 150 and 199 things unlocked, because there's a trophy for 200, and it's the last one I need.
It misses that delight of "I am become death, destroyer of worlds" that I could often reach in VS, but it's very good overall, and definitely worth the $6 I paid on sale.