As aliens coming up through the floor proved to be quite a popular idea, in 4.2 this happens more frequently, meaning you are never quite safe from the alien threat! In this patch there are also more weapons, and - finally - the ability to close doors!
MORE NEW WEAPONS
NEW: 8 new weapon types
MORE ALIENS COMING UP THROUGH THE FLOOR!
NEW: aliens now come up through the floor more often and at random (rather than just for missions)
SECURE THE DOOR!
NEW: close doors with 'right-click' or 'o'-key
NEW : mouseover info for aliens now includes health, attack damage and attack type if player has previously killed aliens of that type.
MOD: shooting an alien on same tile as trap now triggers trap
MOD: aliens hatching from eggs are less dangerous types on average
FIX: bug where shooting at teleport trap teleports self
FIX: incorrect mousehover info for 'open door' and 'floor with hazard markings'
FIX: ability to dual-wield no longer affected by 'to hit' penalties, e.g. from illness
FIX: error in number of targets in mission description for 'drone virus' and 'plant life' missions
FIX: scanner sound effect not playing for some scanner types