Space Ninjas, in Space.
I've been hearing about Warframe for the better part of the year in one form or another. At GDC I attended a talk on AI that discussed how Warframe built its levels procedurally and matched enemy spawning to level objectives. At E3 I previewed it, running around on an ice planet in the game with a ton of weapons and powers unlocked, getting to see it playing on the PS4 in its early days. At the time they were running at about 48 fps but targeting 60. Of course, it's looking quite smooth now, with the occasional frame drop here and there I've come to expect from online play.
As a free-to-play game on the PS4, Warframe joins Blacklight Retribution as the first available for the console (with Drive Club having been pushed back to next year). It's probably coincidental, since Warframe has been out for the PC for a while and would have been in development at the same time, but it feels very similar to Mass Effect 3's awesome cooperative multiplayer.
You are a member of the Tenno, a race of beings who have been cryogenically frozen for millennia. You are woken as the Grineer are expanding their empire into the galaxy. As a member of the Tenno you have access to the advanced Warframe technology, basically The Ninja's suit from Metal Gear Solid. You run and gun through procedurally generated levels, collecting credits.
Warframe has a soft story built into it, where quite a bit is not explained up front. The Tenno are fighting to reclaim the solar system from an empire of cyber-dudes and corporate ro-bros (the Grineer and The Corpus, respectively) and the Flood-like forces of The Infested, which are sort of zombie-borg-ish, I guess? It's not explained in gameplay, really. Encounters with these enemies build as you move from planet to planet throughout the solar system, from space stations and ships to surfaces, as you reclaim it for the Tenno. It's sort of implied, at the very least, that all these races were at one time human, but nothing discrete is said.
Anyways, Warframe is all third-person run-gun-slash-slash-repeat. Maybe you use some special powers once you unlock or buy them, but most people follow the basic run-and-gun philosophy. As you fight, you gain greater "affinity" with your equipment, in addition to regular leveling to increase your baseline stats. So as you level, your warframe, firearms, sword, etc. level with you.
A lot of stuff can be bought fresh-out-of the box in Warframe with platinum, which you can buy for real money. Alternatively, playing missions earns you credits, component drops, mod cards, and rare drops of blueprints which can be used to forge the items you could otherwise buy in the game's Foundry. Blueprints can also be purchased for credits from the same store that you can spend platinum to buy the items outright. The tradeoff, like any free-to-play game, is time. To forge a sword that's a little better than the default one, which I found a blueprint for, took 12 hours. Of course, you can continue to play the game during that time.
Gameplay-wise, it's actually too bad how similar Warframe is to Mass Effect 3's multiplayer, because it really shows the chinks in Warframe's armor. There's no selective targeting feature for enemies, which means that attempting a melee attack, one of the features that the game is clearly built around, can easily overshoot or miss an opponent, and then leave the player spinning wildly as they try to connect with a close-quarters attack. Instead of a targeting features, the game auto-locks onto an enemy's chest when your targeting reticule gets close (no thank you, you're inhibiting my ability to headshot), but this feature can be disabled.
At one point I disabled the HUD, because I loved the clean look of the game without it, but without a map it was too difficult to see where I wanted to go. Warframe looks next-gen, with clean textures, super-futuristic lines, and a smooth framerate. Everything is just gorgeously designed and has an original look and style that helps sell the soft-story. For instance, when you leave a finish a ship mission, you step into a mold for your body and then the wall separates and pulls out of the room, and you can see it's part of a dropship that only needs to hold you in place due to the advanced tech in the suit. However, back in the beautiful level, without a map, it quickly becomes clear that it's impossible to tell where to go. Sometimes even with the map it's impossible to tell where to go.
Player training is not Warframe's strong point. At one point it was necessary to shoot out a ceiling fan, run up the side of a wall and hoist oneself into the ceiling. But this was never covered in a tutorial. With the map in 2D, it just shows where you are supposed to line up, but not what elevation your objective is. In another game, a group of other players and I spent ten minutes trying to jump onto a tree branch to cross a chasm, only to fall continuously into a pit and die, because there was no introduction to the wall running mechanism we were supposed to be using.
On level design things generally work, although since Warframe is made up of different modular pieces that are stuck together, it can start to look a little too similar. And you will occasionally find paths that in previous levels sped you on the mission objective have invisible walls of force that blow you back or suddenly lead to nowhere, like the back of a staircase. This is fairly rare, but it does sometimes happen.
As far as free-to-play goes, Warframe is one of the most even-handed games I've ever played. At no point playing it did I feel compelled to purchase items with real money. On the other hand, for just 200 platinum, that one frame looks awfully good. Warframe *is* fun, especially once you begin to level up and customize your warframe or forge new items. It also incentivizes you to play as only an MMO can: When you see another player with a gold and red frame, with wispy floaty tails coming off the shoulders in different colors and a matching sentinel, a floating turret that fires on enemies, it's not hard to sit there and go, "Well, I want that!"
Warframe, which has been out for PC since March, is free-to-play on the PS4, and in spite of its bugs, is worth the no-cost price. Playstation Plus members get a free starter pack, but beware that it will get you used to how seductive the ease of purchases with platinum can be.