If you decided to give this game a try maybe you alrady noticed that it's a low budget indie but still I belive it's worth to play. I finished the game and this are the things you should know to get a smooth experience. Hope it will help.

There are several types of weapons divided into 3 category: Blades, Guns and Launchers.
Each weapon have fixed stats wich means if you find 2 weapon with the same name they will have same stats with only difference in level and Ability. In other word, no: the weapons aren't RNG.
You shouldn't upgrate to the max any weapon aside from the "Ultimate" series wich you'll find in the last stage of the game, simply because it's a waste of money and upgrade gears with no long terms benefits. In my opinion when it comes to blades I think the Saber it's the best one since it offer great attack speed, fairly low stamina consumption and have a great power. For the rest it's up to your playstile.
Remember: DON'T waste either your money (upgrading or buying weapons) and your gears because if in the early game you'll have plenty and upgrades will cost little you'll find yourself in great need as soon as you'll approach the end.
There's another thing you should't buy: Weapons Mod or Attachments (the two mod you can attach on each category) this is because you'll find plenty. Aim for those who have an Ability, better if green or blue. The ability are always active even if you are not atcively using the weapon they'are attached to. For exemple: If you equip "gain 2HP when kill an enemy" on your rifle but then you use the blade you will get those 2HP anyway.

Don't be afraid to spend your skill point since you can reset your skill trees for free any time you want by talking to Hisako in the train.
Considering that the sword will be your best friend for 90% of the game it makes sense to spend some on this very reliable tool. Let's see what the tree offer:

Whirlwind: It's a waste of skill point since yes it is powerfull but it makes time to load and costs way more stamina. later on you'll be able to deal as much damage with less stamina consumption and faster than the whirlwind;
Lightning,Durable Sword, Sharp Sword: Those are the must have for your sword since they are flat upgrade for any kind of blade you'll find;
Backstab, Assassin: Backstab will be mandatory at least up to Lv.4 to grant you access to the next branch but most of the time enemies will face you and you will not have time to dodge and get behind them especially because you'll be swarmed or closed on both side so it's better to have a good frontal flat damage. On the other hand the Assassin skill makes crits easier wich is well paired with the Passive ability "Critical Damage Up" especially because crits on their own doesn't deal that much extra damage.
Breath of Spring Just 1 point here will be enought and will give you high benefit. Feel free to put even 2 but more than that early game will be wasted.

For the guns the best you can get are the Trigger Happy for fast fire rates Tactical Reload that gives up to 50% to instantly reload a gun and Hunter wich will grant you up to 20% critical rate with your guns.
Thoughness will buff your health and make you more hard to kill
Accelleration and generally the Low Stance skill will be useless since especially later on when you'll meet stronger Mutants and other types of enemies you will not have time to duck down and shoot, you'll run and gun too busy dodging the many many things that will fly in your direction.
Combat Roll: No need for this if you have a skill that we'll see in the next branch.

On the Launcher branch you'll find some usefull skill such Survival that will upgrade your stamina and Combat Readines wich upgrades max Health and Reload Speed.
Another good skill is Runner wich makes your stamina regen quicker making Combat Roll useless.
Fortitute[/b: You may think this is an OP skill giving you an extra life but no it only gives you back up to 20% of your Health once when you die. Late game this means you can last 2 or 3 more blow. Not a good deal, just get good at dodging and flat out enemies before they do it to you.

The map despite looking like a metroidvania is very straightforward and you'll not need to go back.
The best option is to collect everything to get some bonus stats and then face the boss and go to the next location.
Sometimes you'll find Red Crates protected by powerfull enemies: those crates offer just the same weapon you can find anywhere else plus a lot of gold and gears. Later on they will not be worth the risk or the time.
Same goes for the Rare Enemy (a mummy-like mutant) it's always around Lv.40, doesn not attack and if you kill it you get gold and gears and nothing more.
You'll find some unique weapons too while wondering around: don't bother wasting your money.
Puzzles are quite easy. When they are not plain explained just take a look around you and you'll find out the solution.

First time the boss may be a bit confusing especially some of them but don't worry and don't give up

1st Boss: When it's green go behind him and beat it, when it's red it will jump and make an explosion. Just jump twice to dodge it and chase it or shoot from distance;

2nd Boss: It's dumb, just beat it;

3rd Boss: You can dodge most of it's attack by reaching the high spot (higligted in blue), occasionally jump to dodge the rest and wait for the moment;

The rest of the bosses are quite easy in my opinion aside from the cocoon. With it it's faster if you just shoot the "spot" insted of chasing the "weak spots" that will spawn around.

The final boss... I can't say much without spoiling so just one hint: A vey dumb and efficent way to kill it it's... just hit it with the sword. But be carefull: just like the average League of Legends player it will occasionally outrage and will deal damage to everything around him.
Sometimes happen just at the start of the battle that the boss will initiate the animation for one of its jump attack but insted it will instantly teleport on you and deal damage. It's a glich, it will happen other times to with enemies with similar attack.

That's it. That's all I think you should know. I had fun with this game and I wish you'll have fun too.
For anything else just leave a feedback and I'll see what I can do... If my memory still manage to remember the game.

....One last thing........toss a prize to your gamer oh abundant Steam Community ( :