1. Graphics Rendering: One key difference between Amethyst and pygame is their approach to graphics rendering. Amethyst uses a modern graphics engine based on the open-source rendering engine called gfx. This allows for more advanced graphics features and effects compared to pygame, which relies on the SDL library for its rendering capabilities.

2. Entity Component System (ECS): Amethyst utilizes an Entity Component System (ECS) architecture for structuring game entities and components, providing better organization and scalability of game objects. In contrast, pygame does not have built-in support for ECS, requiring developers to implement their own entity management systems.

3. Supported Platforms: Amethyst is designed to be cross-platform, allowing for game development on Windows, macOS, Linux, and even web browsers through WebAssembly. On the other hand, pygame is primarily targeted towards desktop platforms, limiting its ability to deploy games on a wider range of devices.

4. Performance Optimization: Amethyst places a strong emphasis on performance optimization, leveraging features such as parallelism and data-oriented design to maximize efficiency. While pygame is capable of delivering satisfactory performance for simpler games, it may struggle with handling complex computations or large-scale simulations due to its design limitations.

5. Community and Documentation: The size and activity of the developer community surrounding Amethyst and pygame differ significantly. Amethyst benefits from a growing community that actively contributes to its development, providing resources and support for newcomers. In contrast, pygame has a more established but relatively smaller community, which may result in slower updates and fewer readily available resources.

6. Learning Curve: The learning curves for Amethyst and pygame can vary for developers with different backgrounds and skill levels. Amethyst's use of modern game development principles and Rust language may present a steeper learning curve for beginners, while pygame's simplicity and ease of use make it more approachable for newcomers to game development with Python.

In Summary, Amethyst and pygame differ in graphics rendering capabilities, ECS architecture, supported platforms, performance optimization, community size, and learning curve, making each suitable for different types of game development projects.