I played all the previous installments of this game. So I can tell that this add a little to the franchise. However, it is good to have 12 hours every year to play this series. Why? First, the acting, to get into the characters that are, in the perspective of this genre, well-developed. Second, the game feels long, but you never get bored because it has a good pace. Third, Gears of war tends to be the best looking game for Xbox console.
In Normal difficulty is not difficult at all. So I recommend to not play it in easy.
The game has 5 Acts with several chapters (3 to 6). Some chapters are pretty short, some pretty long.
I do recommend to give it a try if you haven't, but I also do recommend to play previous installments before trying this one. The story is connected in many ways so you won't be lost any time.
Achievements are not easy to get, at least for me. I am not trophy hunter but this time you get a little for only betting the game. I didn't try multiplayer because I don't have good internet service and I don't have time if I get really involved. I mentioned this, because, part of the appealing of this game is the multiplayer, something I am missing in my review entirely.