Thank you so much for your kind feedback! I really appreciate it.
In terms of visible trail (path prediction) for bullet - there are currently 5 weapons in the game - 2 of them have non-deterministic path (the ray angle has one of 7 values), there is one weapon that has a ray - sniper rifle. Also laser kinds of give you very specific feedback on how the path looks like as you can see the beam.
In case I misundersstood your point and you ment just the graphical trail after shot - I was actually trying to implement it but I failed :D. I just couldn't make it look "natural"? I experimented with line, particles and so on and just couldn't make it "work".
In terms of difficulty - it really depends on which achievements you want to focus. My previous game received feedback of being too difficult and I thought it may actually be good idea to make the death "non-punishing". Of course if somebody wants just to rush through the game - as you say just pushing forward, making direct fire exchnage - he/she can do it but there is no way that somebody will receive "careful" or "pieceful" achievement in the game doing that. I tried to make the achievements very varried encouraging different types of playstyles :).
Regarding the save files - thanks for spotting it out! Have you played the online version or did you download windows version? :)