AoE4 is being developed by Relic Entertainment with I guess oversight from Microsoft's World's Edge. I don't know if it's good or bad, but it's definitely on my radar. Verdict: probably not an indie game.
Project Zomboid started really small and is currently a collection of very small teams. It's a better "zombie survival experience" imo than a lot of AAA managed to do, even before mods. Verdict: about as indie as it gets without being one guy in a garage.
You were talking up that other game's realistic zombie stuff, and then said you wouldn't touch Zomboid because you were laying off the zombie stuff afterward? The real reason I guess is you can't look past multimedia presentation. I get it though, Rimworld is by all reports from friends, who like the same stuff I do, an amazing experience. Very rough to look at though. I actually have a copy but haven't played yet.
Zomboid hits a lot of right buttons. Sense of doom, increasing necessity for nomadic behavior. Customize most every aspect. Virus infectivity/transmission, zombie behaviors/capabilities, do items respawn or not, when the power shuts off, when the water shuts off, food decay, and more. It's not always glamorous, unless your character somehow enjoys carrying dead zombies to the funeral pyre. Rotting bodies don't make the best company.
You are on the way back from a trip to the burnt-out supermarket you were able to salvage some canned food from. It's the middle of the night (you should have cut it short earlier), in a pea-soup fog. The last zombie you hit knocked out the remaining headlight on your car, so you are slowly navigating back home mostly by feeling out the bumps of the zombies you previously ran over along your usual route.
You just begin to drift off the side of the road, and bump into a tree before you can correct. The engine dies. Great, it just started to rain too. So that's it until you can repair, swap parts, or find another ride. With some sense of urgency (noise attracts zombies), you leave most of your haul and the comfort of the heater behind, and set off down the road with the flickering, yellowed light of your dying flashlight for company.
The seasons are shifting and you're cold, tired, hungry, and depressed. Your bandages, shoes and clothes are filthy, but you have plenty of spares at the farmhouse if you can find your way there. Your civilized life as a history teacher and moderator of a porn subreddit didn't do much to prepare you for the things to come. You cut your hands on glass while fleeing a corner store. You're not sure if you patched yourself up right, and the dull pain won't subside. Your thoughts darkly wander while chewing on a hard aspirin. Ammunition is getting scarce, a mixed blessing because shots clue the horde into your location. Hopefully you'll remember to save your last round. There is always that option, and you are not about to let yourself become one of those things.
The barking of a dog in the distance brings your mind back to the task at hand: make it to the farmhouse you boarded up and sealed. You can barely feel your legs, and hope you'll have enough energy left to climb the sheet you left hanging out of the second floor, make your way downstairs, and start a modest fire. You can hear the faint noises of what might be undead shuffling around out of sight in the bushes. Hopefully, your walking dead edition baseball bat that your dad bought you before this all went down will be able to handle any stragglers before it too breaks.
You stop to straighten your tacticool backpack for what feels like the thousandth time. The canned food is bulky and the thing doesn't do a good job of distributing the weight. The tomato soup is wreaking havoc on your lower back.
A chill runs down your spine as a helicopter, the first one in weeks, flies past overhead parallel to the road. You are all too aware that this attracts wandering packs of zombies, and no doubt a bunch are headed your way now. You have no choice but to fuck off into the tree line and take your chances finding your way back in the bush. If you survive the night, maybe you can go see if they were flushed out of the neighborhood they were loitering in earlier. You have the short rest of your bleak life to look forward to.
At least the rain is letting up.