Reach does not feel like a Halo game.
Jumping in Halo has always been fun. Decent height, and a smooth gliding feeling on the way down from peak. In Reach, you have what feels like the shortest jump in the series, and instead of a smooth rise and fall it feels like I'm under a soft ceiling. Several times I honestly thought I was stuck under something: it feels like I hit something and then drop down fast, distance truncated. It's not fun.
That kind of little change carries through to the movement and gun play. None of the guns felt powerful or fun to shoot, and I had a hard time telling when I was landing shots. I still haven't put my finger on why, but shooting someone in the Halo games has always had this really strong feedback loop where I felt the shots landing. In Reach, that's not there. I shoot, the guy falls down, move on to the next one.
I wish I could crystallize it better, but it just doesn't feel like Halo. It looks like Halo, has the best menu and interface I've seen (though the CTF UI is really confusing), but if the exact gameplay and controls were mapped onto a different looking game, I would not think it was Halo. And I love Halo because of how it feels to play. This thing feels alien to me.
Maybe I'll get used to it and learn to love this other, new game that's called Halo but doesn't feel like it. I hope so. But I'm honestly just in a state of shock at how the game plays. This ain't Halo.