Smackdab is still in very early development, and actual gameplay might change in the future, but currently it is a better remake of the game, including spine animations and (slightly) better textures.
The main thing about Smackdab is that it is being built for multiplayer support. (Local currently, but online planned)
The characters look very similar to the original characters and the only two weapons currently in the game are the Pistol and Tesla based off the weapons in TSINROF.
Here is a screenshot showing off the new gui, weapons and multiplayer: