>>4992435
Freelook wouldn't be like originally intended, but using the mouse for horizontal turning is 100% legit, that's how Romero played and recorded the original main menu demos, and tested levels.
That said, if you've beaten Doom and Doom 2 before, the legit way, and you're moving on to Final Doom and megawads, I'm not the kind of person who would hold it against you for turning off auto-aim, putting on a dot crosshair on the screen, and using freelook, mostly because that's THE way to play first person shooters, it just feels right. Final Doom generally feels nicer to play without auto-aim and with freelook, at any rate.
Staying straight, don't use freelook to shoot at shootable switches the map author wouldn't expect you to be able to shoot at until you reach his intended placement, that would be called Breaking Sequence, and you would kind of be robbing yourself of the intended experience that way.
Same for jumping and crouching, if that's something you like, go for it (it can be useful for combat on occasion), but mind that 99% of all levels people make for Doom are not intended for you to jump or crouch, so jumping up on ledges, crawling down through small windows, or clearing a gap you couldn't expect to just run across, would be Breaking Sequence. Use your own judgement I guess.