On the other hand, there were a bunch of missions that could have been a lot better with very simple adjustments. Some of the levels are way too easy, even on brutal, and some of them just could have felt a little better. Here are some thoughts on things I don't really understand from blizzard's thought processes behind some of the specifics on some mission.
Lab Rat: It would have been nice if there were a few bots attacking your base at the start. I understand that valerian was unprepared and that's fine, but not that unprepared (this is small though).
Back in the Saddle: The timer is wayyyy too long for the security lockdowns. When you control only one unit, at least try to make that difficult.
Rendesvous; now this is an interesting one. I feel like it should have been a timed level when I was playing it, but I suppose Jim never arrives there, so blizzard gets a pass on this.
Domination: This is way too easy. Even on brutal this is easier than the equivalent Warcraft 3 mission (Mal'Ganis one) on normal.
Old Soldiers: I suppose I understand that blizzard wanted to be noob friendly, but this would have been a nice place to introduce overseers and have then nuke your base from time to time...
Harvest of Screams: This mission should be timed, possibly with your time increasing every time you kill a spire. The way it is it's as if the spires are fake and not actually contacting shakuras, as you have a million years to kill the protoss here.
Waking the ancient: Way too easy, even on brutal. The primal zerg need something to counter mutas.
The Crubicle: Nice level, but why is this a swarm host level? Swarm hosts aren't very good in the campaign, but this is the worst level for them in the game!
Infested: Losing a virophage is kind of meaningless in this mission when you can replant them in 2 seconds with an infestor. They should either take a couple minutes to respawn or be one shot virophages only.
The Reckoning: Right before the mission, Kerrigan agrees not to attack any civilian centers that are still being evacuated. It would have been difficult to design a mission around not harming civilians while invading the planet, but that would have been interesting to watch. Have mensk march the Oden through a civilian center that you aren't allowed to go in, destroying all the cars and people in the region? I don't know, I just would have liked some gameplay aspect to support Kerrigan's sudden caring about civilians in the end.
Also, Kerrigan is ridiculously overpowered. Heroes should be good, but not that good.
On a side note, I think the duran/narud missions were kind of wasted potential storywise. Blizzard did an amazing job building him up in Brood war, and then, bam, we just discover him hiding in a lab and then we kill him here. I expected him to be a bigger part of this game, and was kind of surprised/disappointed that he died so easily.
As I said, I love this campaign overall, but I think there are a few simple things that could have made it a lot better. What do you guys think?