This is exactly what I wanted out of this campaign. Just enough story to hang things together, but the focus is on crazy combat encounters and replayability and mastery, with a nice mix of offensive and defensive objectives. Battle spaces are suitably large and/or multi-layered, and you'll need to watch your flanks and rear because you can never be sure what the game is going to throw at you, or from which direction. You *will* be caught off guard if you're not keeping your head on a swivel.
Playing solo is absolutely do-able (am doing my usual first run on hardcore, no declassified missions), but you can tell every bit of this is built for and shines in co-op. Friendly AI is quick to recover you, but enemy AI can be suicidal in their single-minded rushes to take down whatever they determine to be enemy #1, even if that means running right past other gears.
So its not the cat and mouse risk/reward of moving cover to cover and rushing of Gears 1 on legendary, but bite sized, intense combat encounters, one after another without all the slow walks and cut-scenes.
You get scored on each checkpoint, which is very frequent, but I'm not sure whether the model and skin unlocks you gain by leveling up are purely for multiplayer versus or not.
Mood is Gears 1, with the colors and scale of Gears 3, and the action of Horde, only mixing both assault and defense to keep things interesting. To rank up and unlock Aftermath you need stars, so that means not getting dropped, taking out groups with heavy weapons and frags, headshots and executions for decent scores.
So far I'm loving it. Won't know until I replay the campaign with different difficulties, objectives and solo/co-op whether this has real legs to it, but its been a fun, smooth, gory ride.