There isn't much information on Cloakers, but you'll hear "a faint hissing whine" when they're in proximity. These light machine guns, while having a large magazine size, take a long time to reload and slow you down by 20%. Knives, on the other hand, introduce a new charge attack that can knock down enemies, so the longer you hold down the melee button, the stronger the attack. Finally, the new Gage weapons pack adds four new masks into the mix, along with new patterns and materials to customize them.
The Gage weapon pack 2 DLC will be available on Steam in February for $5. Along with the new gear, the DLC also adds a handful of new achievements, which you can review over on Overkill's site.