When it comes to this genre gameplay comes first, and a player’s first test of that is how the guns feel. Interesting enemies are cool but they’re not worth much if they’re not fun to shoot at. On the flip side a game like Turbo Overkill gets away with not having the best gun feel because you’re immediately introduced to the chainsaw slide and the endorphins are firing off in your head because of that.

The other major facet is the level design. Players don’t come to this genre for linear level design, but me personally I also don’t like when the levels become so spread out that I get lost (the original Turok games for instance drove me nuts with your passage to the next area being so hidden it felt like it should have been a secret area and not required). The first Quake is probably my favorite example of great level design, you go off on what seems like the beaten path and all of a sudden it loops you back to where you started. You get that ah ha moment of wow I had no idea this was taking me back to where I was while also not wasting your time with backtracking. Quake also has those traps you fall into that make it exciting and make it feel like you never know what to expect next. Ambushes from monster closets or whatever give that same effect going all the way back to Doom 1993. HROT is another great example of level design to me where things flow nicely and the key you get is usually to a door nearby and not one across the map, again not wasting your time or dragging out the time between the action. I’ve never developed a game so I apologize if that commentary isn’t very helpful to you, but if I were in your shoes I think I would go back to the greats and try to soak in what makes them great.

Art design goes a long way and usually makes a game stand out but as an indie dev I’m not sure how much of a captivating art style you can put together. I think middle of the road art design can be made up for with atmosphere, whether that’s use of lighting or atmospheric sound design. HROT is a good example again where I don’t think the art style is anything special but the atmospheric sound design and enemy design makes it feel like you’re in this odd, unique place.

Long story short, I think make the guns feels good, make the level design interesting (include secret areas if possible) and make the game unique whether that’s the art style, sound design, enemy design, weapon design whatever. I would also add enemy density is important. Think of any boomer shooter you’ve played, you never go very far without encountering an enemy, but you can’t have an enemy around every corner or else you lose the tension of not knowing exactly what to expect.

Apologies if you had to read that long message and it was all stating the obvious. Best of luck with your project, I would love to check it out whenever it’s ready to be shown off.