The good part is see a literal wave of zombies break upon your defences. Haven’t seen anything quite like it since Starcraft 2, and here they took it to the extreme.
The bad part is that all the missions start the same, which just your HQ, so the first 10-15 minutes are just going through the motions.
The good part is that the way global upgrades system works, is that after every mission you get to pick at least one upgrade. The bad part is that some upgrades are just not very exciting, like +5 to the HQ sight range 🤷♂️
The good part, is that almost every mission has some idea behind it. Here’s a canyon, where zombies can come only from two directions. Here’s a peninsula, where zombies arrive only through a bridge, but in a huge wave.
And here’s a map that has no natural defences whatsoever, but you have plenty of time to prepare.