Just finished it (yeah, I know, everyone else finished it a week ago, sue me). the story is decent, and delivered well. Good actors make all the difference. And while they leave room for sequels, its not a cliffhanger per se. If you are gonna tease me with a sequel, do it this way. Not Hal2 cliffhanger, no resolved story and wait 4 years for the conclusion.
Sometimes, the control scheme DOES get in the way, you really have to get adept at using the A button, or you will stuck, and then you will get killed. Usually by a Beserker. Some of hte segments are unsually hard, even on Casual, requiring multiple attempts. I am not sure this is a bad thing, and its not insurmountable if you have patience, or better yet a friend.
Which brings me to coop. Holy **** did Epic hit it out of the park with coop support. I get stuck? Call a friend, pickup RIGHT where I am stuck, then, because its so much fun, continue to play coop. Its seemless. Its excellent. Its the benchmark for all XBL coop games, and a HUGE smack in the head for developers who make shooters like this and don't include coop. I think coop absolutely makes this title. You feel as though you are fighting, and even better when you are fighting WITH a buddy.
I rarely want to play shooters again, and NEVER on a higher difficulty. I want to do both with Gears. With a friend. And then again on Insane (casual->Hardcore->Insane).
If you have a 360, buy this game. If you don't have a 360, get a friend with one and buy this game