Gameplay in UFO: Extraterrestrials is similar to the original X-COM games. The player starts out with a base where they can add buildings, allocate scientists, equip soldiers and vehicles, manufacture equipment, etc. Additional bases can be bought in different countries but are used mainly for housing interceptors. Most buildings cannot be built in bases other than your main base.
The research side of the game is extensive, with about 120 projects to complete. These projects lead to improved weaponry, equipment, and understanding of the aliens.
When a UFO is spotted on the global view (or "geoscape") the player must send interceptors to shoot it down. Once the UFO has been shot down the player can send in a transport of soldiers to carry out a tactical mission to neutralize the aliens and capture their equipment. Alien commanders can also be captured for interrogation.
The tactical missions are turn based, with no real-time option. The tactical squad that is sent to the crash site can include robots and tanks as well as soldiers; tanks and robots take up more space in the transport, however, and space is limited. Tactical missions can take approximately 30 minutes and there are about 200 pre-made levels. When a mission begins a level is chosen according to the environment where the action takes place; the environment in missions is destructible.
The aliens can start a tactical mission if they attack any of the player's bases. Aliens can attack the player's base with UFOs, in which case it is a fight between your SAM sites and the UFO; if the SAM sites are destroyed, a tactical mission within your base will take place (or aliens will take it over in which case the player needs to send a transport ship). The aliens may also initiate a terror mission against any country; in this scenario the environment is a city with civilians in it.
The more aliens a soldier kills the more experience he receives (tanks and robots do not gain experience). There are rank insignias that show this and titles linked with each; when a soldier accumulates enough experience they go up a rank. Soldiers lose experience when they are recovering from injuries in the hospital; they can even lose a rank if they are in there long enough, but when a soldier comes back from the hospital they will gain experience faster for a time.
According to the magazine, the more visible features of Bman's mod are added weaponry, incorporation of the original Enemy Unknown enemies (although graphically by copying and enlarging the older game's sprites), improving AI and rebalancing the game mechanics by changing them towards those of Enemy Unknown.