Hellgate: London combines role-playing game mechanics with first-person shooter gameplay. Although the game looks and plays much like a first-person shooter, characters do level up, receive points to spend into skills or character statistics, and the outcome of a battle is influenced as much by items as by player skill.

High replayability is attempted through randomly generated levels, randomly placed monsters and fully random item drops and modifiers.

Multiplayer is focussed on cooperative player vs. environment (PvE) combat, there will be a simple duel-based player vs. player (PvP) mode, and Elite subscribers will gain access to full-fledged arenas and a PvP ladder.

In multiplayer mode, players can meet and organize for team play and quests in safe zones - the old Underground stations, protected by the Freemasons' wards. The world will not be split in "shards" or servers, but rather play like a massively multiplayer online game with heavy instancing, such as Guild Wars. Like in Diablo II, but unlike in most 'true' MMORPGs, grouping with other players is optional. Every character is capable of soloing the entire game, though grouping will bring benefits in terms of experience gain and items. Difficulty will be balanced much like it is in Diablo II, where the opposition grows stronger as more players play in the instanced areas.

While it has been stated on the PC Gamer magazine that Hellgate: London will support Windows Vista and DirectX 10, Flagship Studios has made repeated statements that the game will run perfectly well on Windows XP and DirectX 9 based systems. The game is said to be capable of running just as easily on computers as old as 4 years with some settings disabled.