Modders with moddb site released a mod Top Down, Half-Life turns into a sort of Hotline Miami. The camera is attached to the ceiling and to be a player, but the basic mechanics of the game remains the same.
Half-Life is not meant to play with the top view. Therefore, for the convenience of the author made two camera modes: fixed and dynamic.
Fixed simply clips the camera at a certain height, how it works in most games with the top view. However, because of this, the player will see all the cards of emptiness, and a low ceiling can hide the character of the mind.
Dynamic camera changes its position depending on the room conditions. The player will not see any voids around the map, but in areas with a low ceiling vision range will be very small.
To make the game easier, the author changed the shooting mechanics, by removing the need to aim vertically. In addition, he increased hitboxes opponents, so get into them has become much easier.
Author fashion is not sure that the camera is fixed on top of all levels. In addition, in the comments the players say they can not kill some monsters and break boxes. If you are not afraid of possible bugs, fashion can be downloaded on the website
moddb. You can install it only on the Steam-version of Half-Life. Unzip the folder HLTopDown in Half-Life directory, restart Steam and you can play.