Chainsaw Maid

Same director/animator, same animation style, same comic-horror tone. If you liked one you'll like the other. 

Both are Claymation projects undertaken by Nagao Takena and are done wonderfully. Worth watching if you have 12 minutes to spare. 

-both are gory -both have a dark sense of humor -both of them are from the same creator 

Both are horror stories about a girls(s) fighting horde of zombies. While Highschool of the Dead is more ecchi, Chainsaw Maid is more of an experimental ONA. 

Both are creepy, bloody, sick claymations made by the same person. 

Both are creepy claymations made by the same person. 

Bloody maids. Hahahahaha. Crrazy and creepy. Chainsaw Maid is one randomness full of gore. My tummy feels funny. Lol. Roberta's Blood Trail is a psychological and thought provoking blood-gore. But you gotta watch this one after Black Lagoon's main series.