Serious Sam 3 is the black sheep of the series and clearly the worst but that's a story in and of itself. First and Second Encounter are much better games.

You are giving a very basic and dishonest summery of Serious Sam's combat puzzles and I'm not sure what linking a bunch of lets plays is supposed to prove? He's playing on Normal for one so the AI is slower and less numerous.

If I wanted to be disingenuous I could simply say 80% of fights in Doom 2016 all you do is circle strafe around arenas picking off enemies but we both know that wouldn't be fair. We both know there is a lot more too it than that.

If you play Serious Sam on harder difficulties there is a lot more too it than just running backwards. Knowing what weapon to use and what to kill first is an important part of the combat puzzle and is especially important. The game does have some fairly simple arenas but Serious Sam has always been more of a 'bullet hell' game where you fight a ton of enemies juggling dodging incoming damage with aiming and prioritizing your targets. If you just mindlessly 'backpedal' without becoming skillful in the combat puzzle you'll just fail every time unless you play on Normal/Easy. That's it's bread and butter and it's okay if you don't like that but there are a lot of people who do.