Warframe has been the only thing I've played for the last month or so, and I'm really still quite impressed with it. We talk about live service games quite often, and where games like Suicide Squad and Concord do it completely wrong. Warframe is exactly the gold standard for how to do it right.
The cool thing about Warframe's monetization is that you literally never HAVE to spend money. You can get every frame, weapon, and every single piece of story content and game mode 100% free. There's a bit of a caveat to that, of course, but the game never puts a paywall between you and the game.
So how does the game make money? A few ways, and none of them are insidious. Cosmetics, of course, seem to be the big one. The premium skins are fairly expensive, usually around $25CDN, but they are really there just for bling value. You can still completely customize your own Warframe with colour customization, and they honestly look great. The default colours available are quite diverse, but you can also unlock additional palettes for a very low price - usually about $1. Equipment in this game is crafted - frames, weapons, companions, even a lot of crafting materials. And that crafting often comes with a wait period while the item is made; usually 12 hours for weapons or 72 hours for frames. If you absolutely must, you can rush crafting for about $0.50. I have honestly never done this, because the time it takes me to get a frame or weapon fully leveled up is usually more than the actual crafting time.
Once your item is actually crafted, you encounter the first barrier I actually feel is something I want to consistently pay for - equipment slots. You have a cap on how many frames and weapons you can own in your inventory at any given time. It's not a hard barrier though - you can leave crafted items in your 3D printer for as long as you want, you just can't use them until they are in your inventory. Additional slots usually cost around $0.50. Again, a very small fee. But you never actually NEED these - I want the luxury of eventually owning all 52 frames, but you can absolutely sell your maxed-out frames for in-game currency and swap them out for the new hotness.
You can also skip crafting completely and buy a lot of weapons and frames directly from the marketplace, but honestly, I feel doing so eliminates a lot of the fun of looking for the parts to build a thing to begin with. This is where the heaviest monetization comes into play, but it really feels like like this spending is designed solely for the sweaties who don't actually want to play the game and just want to be OP without engaging in any of the RPG systems.
And that's... Kind of about it for the in-game spending, honestly. A very common video series for Warframe YouTubers is the so-called "free-to-playthrough"; a start-to-finish run through the campaign and major add-on content without spending a single penny. It's not only doable, but very easy to do. Warframe is the complete antithesis to predatory fee-to-pay live service games, and it continues to see an extremely strong player base 12 years after launch. I can completely understand why. But a lot of publishers see the game's success and think only where they can insert more monetization, not why the lack of aggressive monetization is why the game is so beloved.
I personally don't mind spending roughly $5 a month in small transactions to support the work of these devs. It's a fair trade for me. But if you want an extremely strong action RPG with actually-good crafting and a great story with diverse mission types... Warframe is the best in the business.