I finished all the Spartan ops.
It was a mixed bag and surely something that's better played with friends.
There was a lot of reused maps, but they got better at how they were reusing it in the second half of the ops, with adding some new parts to existing maps and new maps altogether.
The way you respawn as if playing coop instead of going back to a checkpoint makes it way easier, since there's little penalties to dying (apart from whatever weapons you were carrying, which can be an issue if you lose the last rocket launcher of the map and there's still some hunters around); it allow allow to grind through some tough encounters (I played mostly on heroic this time). Though the spawn are sometime either right in firing range of enemies or a hundred meters away.
Another issue is how weapons despawn too quickly, which is compounded by the starting weapon limitations (only carbines and assault rifles from all races available, no shotty or sniper).
Sometime, the game will spawn enemies (like a quartet of hunter or a squad of elites) all around you, leading in an instant kill before you've had time to react.
In the second half of the campaign, the encounters get more interesting, less 'let's spawn a few waves around the player to pad the map length'. There's one with big swarm of promethean drones attacking a position while you activate turrets to help you. Another is a tank session with a lot of promethean drones and knights, so you have to balance destroying the knights attacking you and dealing with the drones respawning the knights and additional turrets, though it is hampered by the stupid tank control (vehicles go where the mouse is pointing) and the very narrow corridors in which you have to drive. Some elites are given promethean shotgun, which is a nice touch, but usually make them less of a threat.
There's also a map with a big vehicle that feel a little out of place, more for something like Gears of War:
Story is also a mixed bag, since what's told in the CGI cutscenes has nothing to do with what you're doing for the first half, since the cutscenes are about a different squad than the one the player is part of. Though in the second half, the story picks up enough that what the player does things related to what's told in the cinematics and I was more invested in what I was doing.