The Witch from Mercury certainly isn't the best anime I've ever seen, but it does a good job at setting up it's second season, and it's beautiful Gundam animations are something to behold. It may end in a way some may find underwhelming, but it assures a second season, which I think heavily entices you to continue watching. I know I'm going to! I think the sacrifices this season makes for setting up season 2 makes this one struggle to reach peak Gundam. It's no Iron-Blooded Orphans, but it's got similar charm.
The animation doesn't really shine until the fights happen. I also don't love that it never really feels like Suletta seriously struggles in this 12 episode journey, but we will see what happens in the second season.
If you're a Gundam fan, this one is a definite watch. If you want to get into Gundam, you should start somewhere else, like Iron-Blooded Orphans.
