Hellgate: London's singleplayer still had some bugs in it due to the developer focusing on the multiplayer online aspect of the game. A lot of the fixes that were in the online version of the game never made it into the singleplayer version before the developers were shutdown.
If you were to go back and play singleplayer now I would suggest taking a look at
Hellgate: Revival. Here are the
Revival SP MOD files. This has gameplay / bug fixes along with opening up previously exclusive content (like dye kits, pets, cube, etc.)
The game shares similar basic design principle with Diablo in that the game is played again through a second time on a harder difficulty. I personally loved the game. Hellgate really shone on the second play through with many "Doom-esque" moments. The Hunter class was basically an FPS marksman class. I thought the Summoner class was pretty fun as well.
Zombies and Exothermic Rifles were crispy fun.