IMHO, Affinity Photo is a great alternative for Photoshop,
much more affordable and yet very powerful. It is a well thought-out application, sometimes even better than Photoshop. The latest Photoshop, for example, even added calculations in numerical input fields that Affinity already has had since its inception. Maybe AP has made Photoshop a bit better.
Competition can be good for innovation.
AP can also use many Photoshop Plugins that people have learned to depend on.
Affinity Photo also integrates well (where applicable) with Serif's other editors, Affinity Design (with a focus on Vector Art, and Web design) and Affinity Publisher (with a focus on Publications), currently in Beta. They all use a similar kind of User Interface (but obviously with targeted controls for the task at hand), thus reducing the learning curve where possible.
The user forums are very helpful, and the moderators/developers also listen very well to their (potential) customers. There is a sense of being taken seriously. Their Video Tutorials are excellent and to the point, also highly recommended for getting up-to-speed and learning about efficient solutions to specific challenges.
AP also has some quite usable implementations of Panorama stitching, Focus stacking, and HDR imaging/tonemapping built into its basic functionality, and it can work with virtually lossless 32-bit floating point file formats (very useful for CGI work and extreme tonal corrections).
Highly recommended, but despite the similarities, it helps to spend time and immerse oneself in the application to get the most out of it. It may offer better solutions to achieving things, and it won't help to attempt to replicate Photoshop's way of doing things. So at occasions, there is some unlearning of habits involved, especially where more powerful possibilities are offered.
Cheers,
Bart