Hey there! I just played your demo and I thought I'd leave some general feedback on it since I really enjoyed some of it, but I felt like I needed to talk about some of the issues I had with it personally. I know from how the page sounds this comes a little bit late to really act on completely, but still, I'd want similar feedback if I were releasing a full game too so please don't take this post the wrong way!
The gameplay was a little hit and miss for me, but that could be due to not playing many games like it. I feel as though generally the game tries to go for a more arcade-like experience, but appears to be missing or off key with certain elements, such as having no score tracking when going through a level or needing to stop and wait for an animation to pick items off the ground. The general enemies also feel far too difficult to avoid for me personally, even when utilizing the dodge roll, which made it feel like taking hits was just inevitable rather than being down to skill or timing to avoid.
I really loved a lot of the art style for the most part, the main cutscenes and general 80s vibe were both great, and even the gameplay itself looked pretty good even if some of the stylizing could've been turned up even higher with lighting and effects. However, I think the mini boss cut ins and character portraits accompanied by text box dialogue were too far removed from both of the previously mentioned styles and clash too much in my eyes. I'd say either go for the cutscene style for both portraits and mini boss cut ins, or use pictures of the in game models rather than introduce a third art style.
The sound department felt like a mixed bag. The music was great from what I heard of it, however the sound effects lacked the amount of punch they required in my opinion, making the guns and grenades feel like they lacked impact overall. This makes the game feel a lot less like the experience I assume you were going for. Use arcade sounds! Make them loud! Make them punchy!
A few smaller issues I noticed that could be fixed are; damage numbers should be larger to reflect more impact with the destructible objects and mini bosses, the crosshair should be visible below objects because it's often easy to lose sight of it such as during the barricade rocket launcher mini boss, and the input to continue text boxes should be more consistent because I could only sometimes move it on with left clicks.
Please don't mistake my entire experience with the game to be a negative one! I actually quite enjoyed playing it aside from what I mentioned, and some little tweaks here and there regarding what I brought up would make this game shine even brighter in my opinion. You've developed something really special and enjoyable here, be proud of that!