Inverted look is a good one. It stuns me that I used to play most shooters with inverted look back in the day, now I'm completely unable to play that way.
Back about 15+ years ago, there was contentious arguments about
Mouse+KB vs. Controller. It basically broke down along PC vs. console lines completely. People who had mostly only played consoles would have scoffed that KB+Mouse a better controlling interface for many shooters. Now-a-days the debate is largely settled because most enthusiast gamers have played both on PC and consoles at this point, and now they get it.
Regarding controllers you still see some contention around
offset analog sticks or inline analog sticks, and that usually breaks down along console-war lines.
A niche debate in FPS gaming used to be between
trackball users and mouse users, with trackball users insisting it was a more accurate input method for first person shooters. It was pretty niche at the time. Now-a-days I don't see that debate very often.
Digital vs. physical games is still a fairly contentious debate.
Sadly you don't see many game vs. game debates anymore because licensing has become so exclusive. The only handful of game v. game debates that could still be around are Forza vs. Gran Turismo. But, back 15+ years ago...
- NFL: Madden vs. Sega Sports series (Starting with ~Madden 95 v NFL 95, culminating with Madden '05 vs NFL 2K5), but also featuring NFL Quarterback Club, Tecmo Superbowl, NFL GameDay and a whole host of others
- NBA: NBA Live vs. NBA Shootout vs. NBA In the Zone vs. Kobe Bryant's Courtside vs. NBA 2K
- MLB: High Heat vs. Triple Play vs. MLB Series ("The Show") vs. MVP v. MLB 2K v...
- Wrestling: WWF (Warzone, Attitude) vs. WCW (WCW vs. the World, NWO v WCW), v. Wrestlemania 2000 / WWF No Mercy
- NHL: Bret Hull Hockey vs. NHL Series (EA series) vs. everything else (2K, SegaSports, etc)
- Soccer: FIFA vs PES vs everything else throughout the years
These were good, stupid, unsettle-able debates in the day, and it's great how some series took over for a while and then fell, etc. But, sadly, because of licensing almost no game vs. game series really stil hold up... MAybe Battlefield vs. Call of Duty is one of the few, but I don't think there's as much tribalism around that as there was over, like Madden vs. GameDay in 1997 or Madden vs. 2K series in the 2000s.