It is a fun game but when I played it i found out it is still a beta and you cannot play it without internet even though it says you can... Overall it is a good game and I would recommend it to a friend
Disclaimer: I have not played the game since just after Chroma was released.
I put between 800 and 900 hours into this game. It was the only game I played almost half a year. I went from playing Planetside 2 to this and was pleased by the different feel of the game - in PS2 you are a small cog and dying is a frequent part of the game (at least for a n00b like me). In this game you feel much more powerful, perhaps absurdly so. As another reviewer put it, Space Ninjas with Guns is definitely a good way to put it.
I don't think I would have put as much time into the game had I not been playing with a clan. It is fun working together to get materials you need. If you want to give this game a try, I definitely suggest you find a group of people to play with.
In this game, you can play as all sorts of different warframes, each having their own strengths, weaknesses, or themes. You can use all sorts of guns and melee weapons. However, the catch is that your account only comes with a couple slots for weapons and warframes, meaning that you cannot have all of your warframes in the closet to choose from the beginning. You cannot have a gun rack full of all weapons from the beginning. In order to expand your closet space, you need to buy extra slots with platinum, which is the in-game currency bought with real-world money. (Why would you want all the warframes and weapons? Depending on how you want to tackle certain difficult missions, you will need warframes with different / complementing capabilities. In my clan, there was one guy who had only one warframe and was thus a bit of a chore to figure out how to fit his one warframe into our battle plans) You can also gain platinum by trading rare items with other players, although this requires a lot of grinding. Eventually you can get good at it, like I did. I only ever spent $10 on this game, and through trading
After about 800-900 hours though, I quit cold turkey. One day I stopped and just never looked back. Why? Variety of reasons. 800-900 hours is a lot to spend on one game. The developers seemed like they weren't really listening to the community, and sometimes had odd ways of trying to fix problems. For example, they wanted to punish players who would AFK and macro. In order to do this, they would take away end-mission rewards for players who spent > X minutes pressing one button at a time...but the problem is, sometimes this is the way you play the game. Also, the game seemed to get even more grindy. Example, in order to build warframes, you have to assemble the helmet, systems, and chassis (and something else I'm forgetting). To get these parts to build warframes, you beat a certain boss and get a random drop. The last Warframe they added to the game before I stopped playing added another level of grind though - in order to build that warframe, you needed to have fully assembled parts for about 3 or 4 other warframes. This doubled or tripled the amount of grind.
Don't let this all scare you off though. I had a blast playing with my clanmates for the 6 or 7 months that I did play. (When I left, they were called Aegis of Elysium in-game.) Again, I strongly suggest you play with a regular group.