Full in-depth review including the story and mechanics didn't fit into steam at all.
https://milkandhate.wordpress.com/2021/05/10/earth-defense-force-iron-rain/

The vanilla game is set up as terrible as everything from japan. I searched for FoV fixes and i think i ended up using the mod from this (https://steamcommunity.com/app/1039890/discussions/0/2270321250022100805/?ctp=5) topic. It ended up being quite fiddly for me (the dawg i forced to play the game with me got it working on the second try unlike me), it often crashes the game on the first launch, but hey, it works. I got proper UHD rendering and injected a ton of FoV to play on my giant monitor. So yeah after tinkering it renders good, even if in borderless mode.

So the game requires 3rd party mods to run on modern screens and to have proper FoV. There are no dual binds or multiple binds in the controls. The game doesn’t run very good. On 10900k\\32 RAM\\GF1080 the game was struggling most of the time a godzilla attacks, dropping the fps below 1. And that even after i dropped my setting to low. Options are pretty weak and several important things are buried in the wrong menus. But most of the time it runs more or less okay. The menus are pretty bad and uncomfortable. In the customization instead of having one item and picking its colour, you have eight different copies of the same item. In usable items instead of picking an item and picking an amount you gonna carry, you have separate amounts as separate items. The loading animations change depending on the story events, that’s cool.

Chikyū Bōeigun always has a small roster of maps, but usually they are so big and get destroyed to different degrees so you don’t notice it until pretty far in the game. It feels like Iron Rain has even fewer maps, and the missions are very short. If you have proper weaponry with sufficient power you are done in less than 10 minutes. And there are only ~50 stages. Since you are playing with weapons you have and not the level-optimal loadout it will take more time than that and the game doesn’t feel too short. But still, the scale of battles and the amount of enemies is much bigger in the last mainline games. Oh, and enemy variety is probably smaller. If you go to the last battle geared for a regular map you will waste probably an entire hour shooting the boss. He has a ridiculous amount of HP. But if you actually decide to have a risky but specialist build you can be finished in ~2 minutes.

Mainline CB games can learn a lot from this. For example that stunlocks are bad. And that stunlocks are bad. But best of all that not having to farm the same stupid boxes for 1\\8th of an HP is amazing. Just outright buying 10000 HP and be done with it and playing the harder difficulties, instead of running normal for boxes until you want to gauge your eyes out and still instantly dying on hard. Unlocking the guns per level instead of stupid boxes is great! But the shop should just go, and so are the gems. If you unlocked it you get it. Not only it removes the stupid grind but allows you to actually try the guns. But the stupid random boxes of the mainline games are still pure cancer, even gems are better than that. Customization is great, having one healthbar for every class is great. This is the best fencer i played even if it has the same weapons as others. Mainline fencer weapons should be less bad.
So. Playing the main campaign and DLC, playing it on disaster is all truly great despite the stunlocks. But going for achievements was a giant chore. Achievements take about 100 hours of thankless grind, mostly of the same one map to get more credits. At least they are all in working condition.