Can someone please tell me how the saving system works (the game's subforum is pretty dead)?

When I reach a checkpoint the game is saved, and I can quit and later restart from that point by loading a game.

But...

when I die and respawn at a checkpoint, does the game autosave then? Overwriting my saved game?

Does it mean that I have to play the full game from level 1 to the end without losing all my lives? Essentailly an ironman game? Other than manually copying and pasting saves outside the game, which I don't want to do.

So far I haven't passed level 1. I lost all my lives, restarted when prompted, and now when I load my saved game, it loads it from the beginning of level 1 (just as if I restarted). There were no multiple saves.

Does it mean when I die on level 2, I can restart from level 2? It's not so bad then.

Yeah if you die and want to load a checkpoint exit to the main menu instead and load the autosave there. Continue will always restart the level otherwise. If you lose all lives in level 2 you would indeed start on level 2 after losing all lives.

OK, I think doing one level at a time is ok. Just as long as I don't have to restart the whole game on losing all my lives I'm fine. So basically when I die I have 2 options:
1) Restart from checkpoint: I lose 1 life but all the enemies I've cleared and all the items/xp I got... etc get saved.
2) Go to main menu and load game. Which basically restores from last checkpoint. I don't lose a life, but since the game is loaded I have to do everything again from that point.

Is that right?

Correct.

I could cry. I reached the final boss and after trying to beat him a few times and dying I accidentally pressed "Restart" instead of "Quit (and load". Yup, have to restart the whole level.

So second time I reach the final boss, beat the final boss (tough battle), I'm so happy it's finally over. But - I say to myself - let me see what happens if I let the timer run out. After all the game was saved after the boss was beaten, and all I'd have to do again is beat the final obstacle, which is fairly easy. I let the timer run out, watch the bad ending and... level restarts and save.

I. Can't. Believe. This.

I *loved* this game. It's great; just what I love about Serious Sam. I don't mind games with checkpoints, if done properly, and the positioning of checkpoints is really good here. But you know, how about letting me load easily a previous checkpoint instead of restarting the level? I think most people would rather restart from a checkpoint instead of whole level, so that should have been the default option - restarting whole level should only be done if user specifically asks for it.

The other minor annoyance is weapon switching. The groups are illogical (different from previous games) and it doesn't save your selection in a group; so if I use the laser gun (5) which I use a lot, then switch to a different weapon and select 5 again it selects the railgun which I don't use that often and I have to press 5 again. On top of all it defaults to the "highest" weapon, which often is the semi-useless flamethrower.

Again, I love this game, but now I have to play the final level for a third time and to be honest I'm getting sick of it. It doesn't help that I get this crash from time to time, the one you get when destroying gas bottles in confined spaces.
https://steamcommunity.com/app/272620/discussions/0/2765630416810753687
https://www.gog.com/forum/serious_sams_bogus_detour/crashing/post3

The worst part is weapon binding is off by 1 compared to the main Serious Sam games. So I kept pressing the wrong key. 3 for a specfic weapon but it's 4 in this game. So strange.

Yes! In the middle of combat it can get annoying.