Helldivers 2

Microtransactions in Helldivers 2 are summarized as...

The game contains a store with a limited amount of cosmetics that rotates a couple of times per week. These cosmetics are purchased using a premium currency, however this currency can be earned in good quantities through regular gameplay as well.

The premium currency comes in bundles that always leave you with a little bit left over. That being said, all cosmetics are relatively cheap compared to other games. Most cosmetics range between 1-3 USD, but since the premium currency can also be earned in-game most cosmetics can be earned for free. You can't realistically earn enough items to buy out the shop every time it rotates, but you just might earn enough for one or two items.

The game contains multiple Battle Passes, with one being free for everyone. New Battle Passes release once a month. These be purchased using the premium currency, which means you can earn it through regular play as well and no purchase is necessary. Earning enough each month does require a fair bit of time played, but it's certainly not unrealistic to obtain every month. The battle passes do not expire with time so there's no rush in obtaining the pass as soon as possible.

Some items in the Battle Pass are not cosmetic only, they provide different weapons or certain gameplay enhancing items for your team.

Premium currencies come in quantities that do not match the price of regular shop items, forcing you to spend more for less.
Includes a limited-time always rotating store with exclusive discounts and/or cosmetics.
Contains one or multiple Battle Passes.
Features unique cosmetic rewards for pre-ordering the game.
Has a "deluxe" edition of the game which features (almost) nothing but in-game cosmetic items.
The original purchase contains all future content, but there are some small optional cosmetics and/or services you can purchase.