There's a rivalry between the two? I guess I learned something new today (and I'm going to doubt it still). Anyway, a nice read.
Never got into Halo; I've tried the first one on three separate occasions, and I've always quit because of how boring it is - and I've played several levels. I don't know what it is, but it's the only shooter I've tried and haven't been able to get into at all.
I'm more of a Doom guy, but I'm not a fan of the newer Doom games. I tried the demo of the 2016 game, and it was obvious from just the demo it had a high risk of being an arena shooter where you have several arenas (rooms) connected together. Judging by everything I've heard, my first impression was correct. It's not terrible, but it's not that interesting either. I'm not sure if Eternal suffers from the same problem, but I prefer to play my games in order - and I can't justify playing something I might only get along with (i.e. the 2016 game) when my backlog is so huge. Also, I don't like how the new Doom games seem like products instead of games with a soul (and it's also a significant problem with other modern games as well).