A list of all official patches can be found here.
A huge patch, it adds support for modern Windows, extra renders, multiple bug fixes, and many other additions. It also includes a patch to allow Unreal to run natively on Linux, however it requires Wine or a Windows partition to get the files.
Installing the Direct3D 10 renderer allows you to play the game in high-resolution, widescreen, and Direct3D 10. There's also a Direct3D 11 renderer, but currently no significant changes from D3D10 renderer. It is also worth noting that the DX10/11 renderer will not work with the 227 Oldunreal Patches; use the built in OpenGL or D3D9 renderer instead.
Various modifications, custom content such as characters, maps, plugins, and total-conversion mods can be downloaded and installed for Unreal. Like every game in the Unreal franchise, there's a ton of mods floating around the web on fansites like Oldunreal.
Maps are custom levels that are created using mod tools or editors.
A complete list of console commands are listed here.
The fastest way possible to run the game on Linux natively is to use one of the Lutris scripts along with Arch Fix one, which fixes the audio issue and for open source GPU drivers it sets the Mesa compatibility to 1999. The script uses OldUnreal's Linux build which can be acquired only by installing the patch through Wine, but in Lutris case it is not necessary as it's included in their repository.
However, as the description notes, you must change the FMODDevices to 27 in [ALAudio.ALAudioSubsystem] section in UnrealLinux.ini (Located in System folder) when you change the settings in-game. If the music does not work, get the 32-bit esound package (Sometimes it can be called esd) from the package manager or download one, run esd in Terminal once, then change FMODOutput to ESD in the same section.
The FAQ for playing Unreal 227 on Linux is on the OldUnreal Wiki.