I'm not sure how I feel about the term "boomer shooter". Given that it refers to new first-person shooters which evoke games from the '90s, shouldn't they be millenial shooters? Fresh from killing napkins and mayonnaise, here come millenials to kill Shub-Niggurath.
This is clearly me fighting a losing semantic battle, but in any case, Humble's Boomer Shooters Bundle has a lot of great games, including Dusk, Amid Evil, Ion Fury, HROT, and more for £9.05/$12.