Thanks a lot for the comments!
-Auto-Shot/ Releasing the shot button : It is true that there is no reason not to hold the shot button all the time, but having it fire on its own outside of a web/mobile environment just feels janky to me.
On the other hand, having the shot button charge an attack when not pressed seems like an interesting idea, though it is not without its balance challenges. The game is caravan-styled so the charge time shouldn't be so long that it becomes counterproductive to scoring to wait until you get the charge shot. I also should be careful not to have the charge shot overshadow the sword or vice-versa. But I can see a charge shot working in tandem with the sword : you would only use the sword for a little while as to charge the shot and then fire it alongside the sword attacks.
Now there is also the problem of the regular shot. As of now, it is useful as a damage boost to sword attacks and as a way to kill the popcorn enemies from afar, but the charge shot shouldn't make it pointless. I could try to test that and see if it breaks the game/weapon balance or not but honestly I am not even sure it's worth the hassle.
As for a wide shot, it is a hard no. The narrow shot and sword ranges were made on purpose to force the player to move a lot to kill every enemy in a wave, even if the movement itself isn't always the most original out there. The bomb having a wider, circular range, is a reward in itself and a reason to take risks to recharge it as often as possible. With an always-available wide shot, you just stay in one place and barely move while everything dies anyway like in Bullet Soul. If there has to be a spread shot though, I suppose it'll be like the Eschatos one which is has very limited forward range.
-BG scrolling : I can try making turns with the camera during those sections but at the same time, that would require to render even more stuff on the screen as to have the BGs not empty when rotating the camera, which probably won't help the game performance. Some of the background events and background setpieces were also made with the lack of camera rotation in mind. You would be missing some train and car movements in Stage 1 for example. In any case, the camera movement turns are not all very smooth and that's something that I am progressively fixing. Maybe that would alleviate the odd feeling a it?
-Wave-independant enemies : Defintely not a bad idea, I'll think about it. The visual issue with ground enemies is that the player/enemies/shots/etc. are disconnected from the background itself and it would look very odd to have stuff that seems to be part of the background while blending in with the air waves. I can still make those enemies behave exactly as if they are air enemies but then I'll have to think of a way to make it obvious which ones are part of the waves and which are not.
-Multi-wave system : This suggestion is actually the system that Radirgy and Karous use. There is one set of waves for the big enemies and sets of waves for the popcorn enemies. I only noticed that after having implemented my own linear wave system.
My system compartimentalizes the waves but it gives me more control over the combination of enemies that spawn on the screen. When multiple wave systems are working at the same time, you can get combinations that won't feel as tight as hand-crafted waves where the big enemy and the popcorn are supposed to spawn together. Radirgy and Karous' waves are fun to defeat but the popcorn waves are a bit generic. You can't make a wave with a big enemy on a part of the screen and one with tons of popcorn elsewhere (to give you different ways to tackle it) and hope they will be synced.
It can still work here too, but there would be a lot more balancing to do I imagine. On top of that, the current wave bonus system shows a point value for each wave that was defeated, a bit like Macross 2's flashing bonus point indicators, as to instill some desire to score. If each independant wave generated its own indicator, things would get a bit messy here.
-Weak spots : I feel like this is actually going to reduce the numer of ways you can kill a wave. Why bother with trying different ways to kill all the enemies when you can only focus on the weak spot? Given how the scoring is based on speedkilling waves, there would be no reason not to ignore every enemy in that wave that isn't the weak spot.
-Shot/Sword power disrepancy : The reason why the sword is so powerful is to push you to use it and play it less safe. The shot is not the main weapon you use against big enemies, otherwise you could just sit back and relax. I can still nerf the sword a bit if its power gets out of hand but so far the dynamic it provides does not feel unwelcome.
-Restart : True! My current dev build actually already tackled that problem and the restart is almost instantaneous now. I used to lazily reload the entire level but now everything is simply properly reset which drastically reduces the loading time.
-Continues : At least unless I find a system that forbids players from just abusing the hell out of them, it's not planned. Scoring penalties are also mostly useless when it comes to deterring anybody from credit-feeding. The game does not run on a arcade machine so I am not even sure of their purpose here. Well, continuing is useful when testing the game though, but there is a stage select (and I should probably add a boss select too, come to think of it)
-Music : Thanks a lot for the link! I'll check it out.
-Slowdown : Noted! I'll probably rearrange the Stage 3's location in regards with the Stage 2, which should allow me to display less objects on screen at the same time in both stages and decrease the camera ranges. Hopefully, that can fix the slowdown problems.
-Boss patterns : The static + aimed is defintely a good way to design boss patterns, I agree. I'll keep that in mind when designing/retooling boss patterns. As for the fast-kill mechanics, there are some enemies that the bosses spawn that can be killed and reflected on them for more damage. The entire third boss is based on this, with plenty of summoned enemies and funnels to kill. If you had the opportunity to fight it, do you think that's a step in the right direction?
-Bullet Count : I don't want to increase the early game's difficulty too much but there definitely aren't that many bullets if you quick-kill waves. Lobo suggested enemies that fire as soon as they spawn to ensure some bullets have to be dodged. I can try implementing that on some popcorn enemies and see how it fares
-Zoom level : GunFencer's relatively zoomed-in aspect is intentionnal. Remember that the game has a 16:9 aspect ratio, so a ship with the same size as a 4:3 game ship would probably be too tiny.
I also don't like dodging super tiny bullets so the bullets are rather big too.
-Pickups : Do you mean the medals are too easy to grab? The cake slices that recharge the bomb are attracted to the player but you have to move near the medals to get them. Should they move a bit faster then?
-Staying on the right side : Definitely a valid issue to tackle. I already have some enemies in Stage 2 onwards that come from behind to force the player to go back to the left side. I have a few ideas to increase that necessity in Stage 2, and I'll put an increased focus on that kind of enemy in the following stages.
-Stage 1 movements : As long as this relatively easy movement strategy is only prominent in stage 1, I don't think it is that much of an issue. GunFencer's first stage's first half only features rather easy to defeat enemies as a an introduction to the game and a way to ease him into it. The bulky tanks only appear after the mid-boss so that's when the movement strategy changes a bit and you have to stay on those enemies a bit longer. Besides, the up and down movement is not necessarily an issue in itself if the wave contributes to the flow. In Thunder Dragon 2, there's a lot of waves where you can sweep from left to right to take them out, but it never feels boring or redundant because the wave composition is not always the same and those waves aren't repeated a lot.
That said, it's still something I have to take into account when designing the waves and the big enemy placement.