Halo just never appealed to me. It has some cool stuff, don't get me wrong, but there's just nothing that got me invested in the series. Keep in mind, I was around when the franchise first started. So I was more than aware and grew up on the impact it had on the industry. Even back then though, I didn't care much for most shooters and only played particular ones.
Between the two, Bulletstorm and Mad World, Bulletstorm has the overall better gameplay and environmental hazard variety. More ways to fuck up mooks. Mad World still has the most distinct design. Pretty much no game can match the black and white style pulled off there.