I'm not sure I'd recommend Ion Fury. From what I hear, the gameplay is great, but the developers might be pieces of shit -
transphobic and homophobic. They apparently had a bunch of shit in the game they'd promised to remove, but after getting review bombed for 'censorship' by The Gamers,
walked back their promise and kept it in. They'd promised to donate $10,000 to an LGBTQ anti-suicide charity as well, but I can't find out if they did or not.
Ultimately, it's up to you if you want to reward actions and companies like that with your business.
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Onto less shitty topics;
Dusk is a very good game in the style of Quake. Very much cream of the crop. The only downside I'd say it has is a couple of the weapons look too similar and there's no BFG equivalent to round out the arsenal. Aside from that, great, fluid movement, good combat, escalating challenge and visuals.
No hitscanners either, which tend to be personal bugbears of mine.
Hedon was enjoyable, and they added a whole nother game length to it after I bought it, though admittedly I never finished that. It's good, making more realistic locations, I guess, that aim to feel more like places where people actually lived and worked - which adds something, even if it means as pure game levels they might not be quite so smooth. Also lots of orc women with sixpacks for those inclined.
Warhammer 40k: Boltgun is, unsurprisingly, a 40k-themed boomer shooter. It's kind of shocking we never got one of these back in the day! It's fast, fun, and extremely nice looking. It runs the risk of getting repetitive, in large part because it didn't really crack the code of making bosses a fun break in the gameplay, but it's a blast for a while and outside of those encounters. Despite a lack of boss variety, the range of regular enemies is great, with several that hit notes I've not seen in other boomers.
To add on to what MoogleEmpMog is saying, Boltgun is closer to Serious Sam in its gameplay still than Doom.
Does Serious Sam count as a boomer shooter? It only came out... jesus, 23 years ago.
I enjoyed it, but I never felt any inclination to replay it once I finished it, and some of the bosses are more frustrating than fun to be honest - it doesn't have any unique bosses, they're all reused, and the Lords of Change have a LOS attack that hits constantly and instantly with not much warning. The guns are fun, but the armour system never seemed all that meaningful for the enemies.
A solid 6/10 IMO.