The recent AOE weapons changes and Wukong warframe changes. Lots of nerfs that were unneeded because, they say, "not enough strategy is used".
BRUH!!!! This is a VVVEEERRRYYY grindy game, AOE weapons, Wukong, and other means were used to ease the tedium of grinding for materials. Why did you nerf the ability/abilities that make the grind bearable!?!? Literally insane.
DISCLAIMER: none of the existing means to ease the tedium of grinding were exploits or bugs or anything. Just existing gear, warframes, mods, abilities, etc paired in such a way to synergize with each other but now they got nerfed for some insane reason.

Apparently some players were complaining that they were joining missions where an OP players were deleting enemies left and right, completing the mission and the complainers could not effectively play the game because there were no enemies to kill. But everyone got rewards at the end as intended...but they still complained. Ok cool, you want to do the mission your way, slower, tactically, whatever. It's cool, more power to you. JOIN A PRIVATE/FRIENDS ONLY/SOLO mission instead of a public one for fak's sake.
I want to do 40-60 missions/hour because the game is grindy and I don't wanna waste my time, that's why I don't leave space for you to do anything. I am basically carrying you, getting everyone in the party, including you, the mission rewards and you complain. BRUH WATTT!?

Now some of you will retort with simething like: how about you and your kind go to private/friends only/solo missions and let the others alone to play at their own pace.
How about no? Lemme tell you why: because there's a lot of people who would rather be carries and get their needed materials in 10min rather than 20min or however long you people would take playing slower or tactically or whatever.
Again, more power to you, I don't hate you, I got nothing against your play style but apparently you got something against my play style. And now we got a problem.

Just good grindy fun!
I have a lot of Prime frames and weapons but I play casually so I can't talk about ultra end-game stuff because it doesn't interest me. Everything besides that is good.

- are very good but I appreciate that the aesthetic is not for everyone.

- will not win an Oscar but I find it to be good, highly recommend.

- is ultra-god-S-tier. LOTS of variety due to many frames(characters with their own set of gameplay changing abilities) and weapons. You can farm everything and stay 100% f2p. Even prime frames and weapons. Nothing is hard gated by premium currency but you can pay for convenience or if you have 0 patience. I'll talk more about this down below.

- is good and crispp.

- should run decent on any old potato.

- VERY VERY GOOD AND FREE-TO-PLAY FRIENDLY.
Premium currency is called Platinum or 'plat', even 'p', for short. It can be farmed ingame as well as bought with real money.

Ingame & website shop:
So most of the things that are worth buying are cosmetics. Yes you can buy frames and you can buy Prime frames when they release BUT (and that's a big but) it's useless to buy a frame if you don't know how to play it thinking you will win the game.
Buying regular frames off the shop is downright idiotic in my opinion because they can be easily farmed ingame. It is my bias as I can't stand people with 0 patience.
Now buying Prime frames when they come out as a package on the website is ok if you really wanna support the devs, and they should be supported because the game is fire. The package usually contains the Prime frame, the frame's signature weapons, Prime as well, as well as cosmetics that are made to fit that frame's design but the cosmetics can be mixed and matched to any frame so that's sweet. If you don't wanna buy the frame access package because it may be to expensive for you then read on...

Player 'shops':
Prime parts for building frames and weapons can be traded and people do it all the time for platinum.
I bought all my Prime stuff (that I didn't farm for) from players using platinum. This is the preferred method for me and I presume for many people. Platinum can be farmed by farming Prime parts and selling them to other players then you use that platinum to buy what you actually need.
I like grinding for stuff but because the daily login sometimes gives you 75% discount for platinum purchases I use it to buy ~12$ worth of platinum which is 1000plat. It's my way to reward the developers given I don't have unlimited money at hand but nobody should feel pressured to spend. If you do wanna spend then even 1000plat @ ~12$ with that occasional discount is enough to buy A LOT of stuff from other players depending of the rarity of the Prime frame/weapon. A super duper rare frame can be 200plat, even so you can buy 5 frames for 1000plat. The reality is that the rarity of a frame does not equal power so you can easily buy a bunch of 30-100plat frames/weapons with that 1000plat. One of the best weapons to make your life easier costs 3-5 plat...you just need to get to Mastery rank 9 to be able to buy it. (that's account level for all intents and purposes, see below)

- pretty good! The game doesn't let you do everything off the bat and stuff is gated behind Mastery ranks (account level, 30 max). That's fine, think like other games that don't let you equip a level 100 weapon at level 1. Mastery rank rises by playing the game. in short: doing the story quests, completing the missions on the map, leveling up weapons and frames...you know...playing the damn game.
It gives you something to strive for because:
-certain weapons and frames can't be acquired/used until you are a certain Mastery rank
-mastery rank determines the starting mod capacity of a brand new frame or weapon or companion, etc
-each mastery rank increases the cap of certain things like daily reputation or focus that can be earned
-bunch of others, warframe wiki is your friend or just pay attention when you rank up.
Other progression stuffs:
-bunch of stuff to collect (frames, weapons, companions, achievements, reputations with their own rewards and gameplay loops, etc)
-beat the missions on the map, unlock harder variants with better rewards (Steel Path, Arbitration missions)
-frames/weapons/companions can be modded. get mods, upgrade mods, install mods to be godlike.
-you can get your own mech (Necramech) AND spaceship (Railjack) to battle in. both moddable as well. The Railjack can even have a little crew of 3 (4 with you included) that can help you pilot and fight. Did I mention that the crew can be NPCs or your friends?
-etc. too much to write here, this is long already.

Lastly this is an instanced game but it does have open world locations. 3 as of writing this review and they have their own stories to tell and their own rewards to give.

Surely I missed a lot but this is getting too long. This game has A LOT OF STUFF TO DO. Give it a go!