I just got Valkyr AND SHES SO MUCH FUN
I was really unsure of Valkyr when I first started with her, but actually, she is a lot of fun once you learn to play her, and you level her up some.
I'm not keen on her 2/3rd abilities (slowing down/speeding up allies seems a little useless, and I can never get her shield-attacking thing to do anything of merit), but her 1st ability is fun for getting around (and hilarious when you get a kill with it), and her 4th ability is very lethal (basically the claw-weapon version of Excaliburs last ability, so therefore slightly slower).
I'm kind of annoyed though that I might stop playing Warframe soon, because I really like to play the game with a friend, and my friend who got me into it seems to be getting distant from it now.
This is quite typical with him. He'll find a game he loves, convince me to play it, get to playing it for a month or so, and then usually lose all interest in it while I'm still in the middle of loving it.