As for over the shoulder shooters, I guess it's just a matter of taste. The graphics are so good in Gears of War (especially the textures) that I thought going with a 3rd person perspective was an interesting design choice. The reason the design team gave was so that the player could actually see their character, and by doing so, feel much more connected to Marcus Fenix and appreciate the design model. It also fit the gameplay better. I prefer 1st person shooters myself, but with Gears of War, I think the 3rd person is ideal, considering the gameplay and art style.
Halo, wow. You don't like Halo...
The first Halo blew me away. I'll never forget it. After trading in my PS2 for an Xbox, the very first game I chose was Halo: Combat Evolved. Needless to say, after experiencing it I couldn't wait for Halo 2. I, too, had been a fan of the FPS genre for a long time, and after sinking my teeth into Halo, all I ever wanted to play was shooters. I have branched off a little since then, but to this day the first person shooter is the genre I play the most (which is pretty much the case with everyone nowadays).
Halo was an incredible experience. The story, the music, the gameplay - it was the total package. The AI was the best I had ever seen in a shooter up to that point, and sticking grenades to enemies and hearing the doomed foe scream out in horror was quite the experience for it's time. I love it and always will.
I am curious as to what you didn't like about it.