My 360 is plugged into a 55" screen. It's not too big for gaming. It depends how far away you sit from the screen, that dictates how much of your vision is filled by the image ("Field of View" or FoV). It's fine for me, not too big at all.
My PC on the other hand has a 23" 16:9 1080p screen. It's fantastic, a nice size mostly chosen because of the space it occupies. Had I a little more space I'd probably go 27" 1440p. Saying that, 21:9 "superwide" screens are a thing now. I haven't seen any in action but I'm very interested as they may be a better way to game. I like the idea of having more horizontal real estate for gaming, it would certainly make it more immersive (though many console ports notably lack FoV options).
Nothing wrong with 16:9 monitor to those naysayers. Everything works perfectly on mine without fail. No program, site, game etc has any issue with 16:9 vs. 16:10. Maybe I'm missing one more (potential) row of icons...oooh. Videos look much better with less black bars, everything else is the same.