Heh. Well I'll try but I think no matter what I say you wont agree; which is fine, different strokes for different blokes.
On top of the fact that Halo is very solid as a FPS in regards to controls, weapons, and vehicles Halo beats Battlefield solidly on two fronts; Game modes (and the customization of them) and casual/living room appeal.
The game modes are an incredible on-up, you can Race you can do your standard death match you can do Team Death Match (very similar to Conquest), Territory (this is Conquest), CTF, Juggarnaught <--- hella fun on both sides, and more soo many more thanks to customization.
Living Room Appeal is something that might or might not matter to others. Its the ability to call over a bunch of friends look them in the face, laugh with them, drink with them, and just have fun socializing over a nice game of Halo.
Yes, this only works if you like Halo to begin with, but you know what? Most people who HATE (yes there is a difference between HATE and 'its a good game but I don't see all the hype') either
A. Believes 100% computer supremecy with FPS
B. Is a hard-core Strategy type, no concessions!
and not having them in the community is not a bad thing
, aka I don't want the n00b I killed with the needler saying "OMG I Would have f*ing killed you if I had a mouse, damn these controlls suck, I f*ing hate the controller" and continues to play two more rounds.
Halo is good, definately overhyped, but it is a solid game. If you dont like it I don't care. Stop bitching and don't play it, simple huh? I'll still have 4 million+ people to play with and I can still be able to enjoy playing BF when I want to too!