You can get the homefront series on steam for ~5$ Ive never played them myself but that seems like a good price to give them a try. Anybody got any other shooters to recommend? I just played through TF2's SP campaign again and it gave me an itch for sp shooters.
Since you said Homefront, I'm guessing your tastes are as much in the gutter as mine. I could post a novel's worth.
First place to start would be pretty much anything by Raven Software before they turned into a Call of Duty factory. Singularity, Quake 4, and the 2009 Wolfenstien are all very playable.
FEAR is also good, and I'm including FEAR 2 and 3 in that. The sequels get shit on, but they're fun. Fear 3 also has some fun co-op if you can find someone to play it with. It's a crime Fucking Run never became a staple co-op mode.
I'll also recommend NightDive's work. They've been remastering classic shooters like Turok 2 and Quake 2.
I could go on listing a bunch. Hard Reset, Judge Dredd vs Death, Legendary (aka Legendary: The Box), Timeshift, and Deadfall Adventures all fit the bill of mediocre or seriously flawed but fun shooters. Or you could play Doom 2016 and Robocop like normal people. It's up to you. (I've not played Robocop yet, but people seem to love it.)
I don't know how many older games would work on modern machines. I know Legendary needs a framerate limiter to stop you falling through the lift in the final stage, and I think Judge Dredd vs Death is limited in the resolutions you can use, and overlays like Steam and Discord crash the game.
And then there's the indies/boomer shooters like Dusk, Boltgun, Ion Fury, etc. I've not played most of them so can't comment, but again, most people seem to love them.