They couldn't come up with a single mission that takes advantage of nydus canals and IIRC you couldn't even build them. The worm bursting out of the ground and disgorging a flood of zerg is awesome, and they could have eliminated the build time without worrying about player vs. player balance and given us the worms from the ground version of all in. I thought that would have been really cool and it was dissapointing when it didn't get used.

It's in the opening cutscene for crying out loud, along with the Ultralisk you almost never get to use.

Also I felt like the campaign was about three missions too short. The evo missions were short and sweet, but mainly short. The zerg characters are also generally much less interesting than the humans (except Abbathor).