Over the holidays I experimented with Immich, especially after they added support for existing folders. These are my initial thoughts comparing it to PhotoPrism.
I find the application quite appealing; it runs more smoothly on both web and mobile platforms compared to PhotoPrism (PP). However, it lacks the polish and some of the features present in PP, such as sidebar options for different views.
The face detection functionality in Immich differs from PP. It works well, especially when identifying younger versions of people. However, it struggles to distinguish between many mother-son pictures, and sister-sister. I adjusted the threshold, but now I have to manually merge clusters of images. It's inconvenient that I can only merge 5 clusters at a time, and there's no way to change this in the configuration. This limitation is frustrating. However, the ability to have multiple accounts and share photos is a positive feature.
I appreciate the story-like feature that shows what happened 'n' years ago, but it's disappointing that others you share the library with can't see it. Also, the mobile and web applications lack consistency; for example, merging photos and getting suggestions for existing names is not possible on the mobile version.
My feelings about Immich are mixed, and I hope the app continues to be developed and improved.