So, I'm going to write a little post here about this game I got sucked into - I should warn you that I don't know everything about the game (yet), but feel I have enough to write a little brief at least.
In its core, it's a solo/coop shooter with RPG elements. You have different frames which are equivalent to classes, each with their own special powers and general type of tank, support and/or damage. That's where the "generic" description ends though. You are "Tenno" - which I assume is latin for "fucking overpowered", and you carry around swords or other melee weapons on your back just in case you want to stab things as well.
The gameplay tends to vary depending on which frame you have picked, anything from straight up ranged, sniper stealth, team support to furious melee, but it doesn't restrict you really as you can equip any weapon on any frame. Now, this is where the RPG elements and "leveling" comes into play, each frame has levels from 0 to 30, as does every weapon in the game. Leveling up the frame/weapon gives you more slots to put "mods" into, essentially augmenting and customizing your weapon and frame to your liking or to your given role for the next mission.
The different combination of frames, mods and weapons imply that there's a relatively low chance of two people having the exact same build, and you can have virtually endless amounts of time planning and scheming on how to make your "perfect" character work. Then you realize you need a "perfect" character for support... and for playing with your friends... and for mission X... and mission Y... and so on.
The missions you do are varied enough in objectives to keep you on your toes, anything from straight up kill missions, assassinations of single targets, sabotage, espionage, base control, defense and survival makes the game feel relatively fresh as you alternate through the various game modes.
The "loot" for some of the longer lasting missions like survival or defense, where you face endless amounts of enemies is also done in a very nice fashion, where you *have* to make it to extraction at the end of the mission or keep the defense objectives alive, or lose all the loot (mods, materials, etc) you accumulated. Obviously the longer you play, the better the loot gets, so it requires a very nice balance between greed and safety.
The game has a F2P with premium currency for sale model, which isn't exactly my favorite, unless it's done flawlessly like in Path of Exile, and to be honest, I'm not too happy with the way they've done things here, but after playing for a while, I've come to realize it's not really too bad. You can pay premium currency to unlock frames and weapons which otherwise would've needed to be crafted through the crafting system. After playing a while, I've come to realize that this isn't a huge deal in my view, as the way to power up the individual frames comes from the mods you place in them, and these can't be bought on the market. In addition, there are better upgraded versions of frames and weapons called "Prime" which can't be bought on the market, so, you still have to do some "work" to get to the promised land.
There's also the option of doing private trades with other players, so you can essentially trade some of your loot with other players for premium currency and so on if you're so inclined to remain a free player but still have "pay" options.
So, just give the game a try - a few hours to pass the first few levels. It's good fun, and if you find that you like it, don't feel bad if you want to spend some cash to support it, go for it! When you perform the first sliding sword-kill, you *should* be hooked! :)
Feel free to use my referral link at https://warframe.com/signup?referrerId=549df5e33846320f3a0bd579
Enjoy the game, remember that it's better with friends, and have fun being a space ninja!