Vanilla game and the expansion pack are fully playable without mods, just tweaks. It is an iteration of 'Unreal' engine, which is not perfect, but not bad. I saw that the 'Elite Force' mod introduces a lot of concepts and mechanics, which can overwhelm a newcomer. All 'PCgamingWIKI' info is relevant for this game. Make sure to run the game with "-nointro" parameter, especially if you have crashes on start. If you also have crashes while trying to change the screen resolution in game menu, edit the game config for target fullscreen display. Apparently there could be a problem on some systems with window rescaling. Therefore, intro movies may cause an issue, because they run at lower screen resolution and also different display ratio than your choice probably.

EDIT: on modern systems, remember to patch all relevant EXE files of the game with 'NTcore' memory utility, as it is a 32-bit game likely to need more RAM due to enhanced setup.