I have played both, and though neither interested me greatly, from what ive seen and heard, the games are not only similiar, but are going to be major system sellers.
Of the two I've only played Gears of War but it feels a little chunky to play. Things like running to cover seem to be designed with the intent of being super smooth but connecting two actions sort of jams a little in the middle.
I don't like the main character much either. All his lines seem to be setup just so he can say something that's meant to sound badass. Although in that sort of game I can live with it.
One thing that struck me as strange is the blood. It looks really, really out of place against the rest of the game (especially when it forms puddles on the ground). It's very strange considering how good looking the rest of the game is.
Dark, I agree with you on everything but the clunky part. I thought the controls and handling were amazingly smooth, and the only time I died due to control errors was when I messed up.