One of the main differences from Linux is BSD's separation between the base system and installed applications.

On Ubuntu, Arch, Mint, etc. there is no such distinction. Everything is made of packages, including the base system. You have packages for the kernel, the init system, logging, networking, firmware, etc. These are all versioned independently and whether or not they are considered "essential" is up to the user to decide.

On BSD, the base system is not composed of packages. It is a separate thing, with the kernel, libc, command line utilities all tightly coupled and versioned together. This allows the components to evolve together, with breaking ABI changes that would not be practical in Linux. This makes BSD better for research, which is why things like IPv6, address space randomization, SSH, jails, capabilities were developed there.

Packages are used for applications and are isolated to /usr/local. Dependency and compatibility problems only exist for packages. The base system is always there, always bootable, and you can count on being able to log in to a command line session and use the standard suite of tools. It is sort of like a Linux rescue image, except you boot off it every time.