Unique game,
from time to time bugged, but devs are trying to fix most of them
real power fantasy -where you are OP

Really F2P, only game where you can earn PREMIUM currency
Playing for 7 years, only bought skins in game, and with in-game trades with other players I earned a ton of PREMIUM currency that I didnt have to buy it with real money. I have enough to buy in game market anything I want.
Only negative side is - in order to learn all mechanics necessary to know- you need to read WIKI warframe page with ton of in-game mechanics and learn them