I've been gaming since 1991, and have gone through favorites during each generation that were on just about every console. But I've grown to love MGS and Halo the most.
Does this mean I have to go with Xbox One next gen? Or am I going to have to buy all the consoles just like every other gen?
You needs only require an Xbox.
MGS games look/run better on Xboxs. Halo can't be done on Playstations.
You could pretend you like another sci-fi FPS exclusive to another platform, but historically that's never worked. That'd be like settling for Atlantic Rim instead of Pacific Rim. Sometimes there are no substitutes.