I, for one, really liked how they constantly changed up the gameplay.
First, in the hospital, you've got your standard Gears gameplay. Then you're on the assault Derrick wreaking havoc on hundreds of Locust, including Reavers and Brumaks!
Then some more classic Gears, this time underground, with a classic sniping moment and many times the typical number of enemies.
Then introduce LIVING cover that you need to feed to get it to move.
Then introduce a new enemy that can revive fallen allies from afar, completely changing the dynamic of those fights.
Then get you EATEN by a large version of said cover, and get you to rip it apart from the inside.
Then you have the bomb part, the 'hardcore' equivalent of getting your dad to help you move your desk upstairs and around the corner while constantly shoving the dog out of the way.
Then fighting on a barge trying to get rid of the other barges.
Then a darn sea monster that you have to make eat you on purpose!
Then a boss fight in an almost coverless area in which you must chainsaw-duel a guy who can cut a tank in half.
Then flying a Reaver and attempting to flee from said boss, only to kill him with rockets and miniguns, Panzer Dragoon style.
Then somehow defending a city that the enemy is trying to sink, just so you can sink it FIRST XD
Then riding a Brumak on an infinite wave of destruction.
Then finally showing how much ass you kick by annihilating a lambent Brumak with the Hammer of Dawn and using it like a bomb. 
EDIT: and I completely forgot about the Tank level, where you have to contend with lots of explosions while avoiding the cracks in the ice!
