ok i have to make an updated review because finding out there's twice as many upgrades is like playing an entirely different game. that's how much of a difference it makes.
DISCLAIMER: i've only played easy mode (it's the easiest to grind for money and achievements), so it may not be entirely accurate on higher difficulties.
i honestly believe i wasn't the only one who didn't realize the other upgrades existed (except the one person who bought them all), and all the game needed was a couple UI arrows to show you can scroll the upgrade menu vertically.
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the biggest game-changer is the luck stat, which makes grinding for money sooo much less of a chore.
before, i needed to reach about floor 50 just to get a couple thousands coins;
i had to grind the game for hours to "max out" all stats that way (which turned out to be only half of them), which was an excruciatingly boring process.
with maxed out luck, i'm pretty convinced enemies drop coins 100% of the time (even if it's not stated anywhere), sometimes even 2, which means you can potentially earn anywhere between 5 and 100 times the amount of enemies you defeat in a run.
they also drop a lot more hearts (which are counted separately from coins; a single enemy will always drop a coin and ALSO have a chance to drop a heart at the same time).
not only does this make grinding upgrades more user friendly, but it also helps with reaching higher floors.
i basically had to force myself to die to end the run, so i'm sure if anyone cared for it they could reach a much higher floor than the current top score no problem.
haven't played any difficulty higher than easy, but i hope the heart drop rate is much lower on those, otherwise the entire difficulty curve goes out of the window because it's virtually impossible to die with max luck (at least on easy mode, up to floor 50).
i legit do not believe anyone has found the luck stat before, because with no other upgrade outside of luck (on easy mode), i got the invincible achievement by floor 25, and when i reached floor 50 (having defeated almost exactly 1000 enemies, just enough for the achievement), i easily had 200+ hearts and 10000+ money, in a single run.
the crazy thing here is that this was always possible (it's not like the latest update added the second layer of upgrades), as the only thing added was an easier way to show those upgrades existed in the first place.
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the sword is arguably the best weapon in the game when used correctly, especially on higher floors.
it doesn't attack far compared to actual "ranged" weapons, but it's AOE is big enough where you can hit multiple enemies at a time, even around wall corners.
to make up for its lack of range, it has the unique trait of being able to repel enemy projectiles.
this only happens when a bullet physically comes into contact with the actual slash animation, so it gets better with improved attack rate (which happens to be one of its upgrades).
its damage output is ok but it's irrelevant since you can also attack with reflected projectiles.
what's really notable about the sword is that when you get a high enough attack rate bonus, it effectively becomes an impenetrable barrier which makes you completely impervious to "direct" damage. any and all projectile will be reflected back, so you can just stand with your back to a wall and watch as the enemies helplessly shoot themselves to death.
its weakness is that it only reflects projectiles in front of you (your back is completely exposed), and rocket explosions will damage you all the same, so if one hits a wall close to you, or you reflect a rocket towards a close enemy, you'll still be caught in the explosion and take damage.
maxed out rifle is just a solid weapon overall; probably the best ranged weapon in the game, especially on easier difficulties.
it shoots a constant and fast stream of bullets, which is useful when you're trying to hide near a corner and you need to quickly dispatch a row of enemies on one of the sides.
it feels like it has the longest range of all weapons, so as long as you can clear out the area around you at the start of a floor, you can probably clear it without even seeing a single enemy.
its only drawback is that it has "weak" damage output, but with high enough fire rate it goes almost unnoticed (especially past floor 15 when you're guaranteed to get some kind of bonus to both damage and fire rate).
don't have much to say about the shotgun, which is unfortunate because i kind of liked it starting out.
on easy it already kills with no upgrades, and the upgrades simply increase its spread and number of bullets, so all it really improves on is the amount of enemies it can hit at once.
it pretty much fills the same niche as the rifle but with a lower fire rate, so it feels like a "worse" version of it.
after trying both the rifle and the shotgun on hard mode, to test whether the increased base damage of this one makes it better overall (due to facing tankier enemies), i can say that neither can oneshot them without at least some floor bonuses, so imo the rifle is still better (though i suppose it's down to personal preference).
only case where i prefer the shotgun over the rifle is on the early floors of insane (since there's no upgrades), where killing enemies earlier does make a difference.
i'm quite happy with the new and improved rocket launcher, since it's not only a liability anymore, and it actually has its own niche.
i always hated rolling it in the weapon rotation before the most recent change, because i had to constantly worry about not killing myself while using it, and increasing its explosion range only made that more likely.
it has a slow fire rate, it's hard to actually hit the bullet, and when it did the explosion didn't even deal enough damage to kill an enemy.
i still think it's likely the worst weapon out of the 4, but at max level the explosion range covers like half the screen (for reference, if you're behind a square barricade, you can shoot into it and the explosion will hit all the way to the opposite side of the wall), and it actually kills stuff too thanks to the damage upgrade.
moreover, i don't have to worry about dying from shooting myself anymore, if i suddenly switch to it while near a wall or enemy (thank you for that btw).
it's great at crowd control, provided you actually land the shot (you can now also aim at a nearby wall to make it easier, without being damaged for it).
i would also like to add that the enemy rocket launcher seems affected by the explosion range upgrade as well, unless it was just that large in the first place.
i'm saying this because i've seen entire clusters of enemies being hit by an enemy stray explosion in the crowd (or when they were nowhere close to the explosion), and i'm not sure if this is intended behavior or not.