It is a wonderful game being that it is F2P. If you work hard at grinding out maps for stuff you can craft great shit that feels awesome when you final get to use it. The variations in play styles and classes are nice too.
I jump back in every now and then but I have a sort of gamer ADD. I can play a game (especially one with no set ending) but after a while something newer and shinier shows up and I spend some days, weeks, or months enjoying it.
Warframe, in and at its core, is enjoyable for what it is and shouldn't be missed by anyone who likes that style/genre of gaming. I got at least 60 dollars of enjoyment of a game I paid only an internet bill for.