I'll be honest; I love this game, love it to pieces. You on the other hand may have a very different opinion.
I would normally say to do a lot of in-depth research before making a commitment to any MMO, but considering Warframe is free, I would say that all you need is a light brush over of what the, in my opinion, pros and cons of Warframe are before trying it yourself.

PROS:
-FREE
-Very Intense action
-Addictive
-Very immersive for a 3rd person game
-BEUTIFUL atmosphere and world design with decent graphics
-Interesting lore that is slowly revealed by community events and progression
-Very good administrative team
-Updates on a regular basis
-Great customization of your arsenal
-Everything necessary to the experience can be done without in-game currency (platinum)
-Runs very smoothly even on the lowest end computers
-Very helpful and friendly community
-Trading system (you can even trade for in-game currency)
-Not pay-to-win

CONS:
-Not friendly to the impatient (Long wait times for crafting, slow progression)
-Very repetitive/Grind-y (missions are clones of each-other with different graphics or gimmicks thrown in)
-Big pay wall as far as anything not essential to the experiance (vanity, exp multipliers, Credit boosts, Faster crafting etc.)
-Buggy as all hell
-Default settings are awful (motion blur... MOTION BLUR!!!!! D:)
-Balancing is off (as far as weapons)

These are, as far as I can tell, the major pros and cons of Warframe. In conclusion, Warframe is a very satisfying and addictive game for those who are into fast-paced action that makes you feel like a complete badass. And although it is not essential, I would suggest laying down about 20 or 40 bucks (or your regional equivalent) just for convenience sake. But please, before putting any money down, play the game for at least a day or two just to evaluate whether it is something you would truly enjoy. Thanks for reading, I hope this was helpful.