The first thing I noticed is that there's really bad player messaging. It's often hard to know what the game wants you to do or even what they're trying to teach you. It led to a lot of frustration right off the bat.
But, I also noticed the fact that I was essentially playing a PVE game as a robot ninja... so I stuck with it for a bit. There's something satisfying in the core mechanics of the game and most of it comes down to that robot/ninja awesomeness.
I can definitely see the possibility of a good game in Warframe but after spending a few hours with it I realized I'm not willing to slog through the bad explanations and player messaging to find it.