Does anyone play FPSes on SP?

Firefall has been in closed beta for almost a year I think. It'll remain in closed beta until the developers think that the game is ready and then they'll just remove the beta tag. Their invitation system is like the way Gmail did it.
There is a lot of important features missing and content that needs to be polished in both PvE and PvP. Before the devs went on their holiday break, they released a patch that increased the tier constraint system limits. If you craft an ability or equip, it will tell you how much CPU, Power and Capacity it consumes. So they increased it with a lot allowing players to test out all types of equipment while they fix the constraints system and separate PvP from PvE gear.

PvE is limited in my opinion. If you see official Firefall trailers, you will see a lot of scripted content. However there are dynamic events such as Chosen, Melding Twisters, Crashed LGVs, Crashed Thumpers and missions you can complete. In the beginning you will most likely create a squad with friends or strangers to collect resources. This can be done through a Thumper. A Thumper is basically a machine that you call down and once it falls to the ground, it will start to drill and collect resources. But when it is drilling it will make a noise and the creatures in the world of Firefall can't stand the noise of Thumpers so your duty is to protect the Thumper from destroying.

They're working on it and polishing content. There are a variety of monsters and bosses out there, even one that requires team work. You can explore and have fun with your jetpack. There are achievements in the game. A lot of content needs to be polished, like crafting. Red5 said they're working on an UI/crafting/profession revamp.
Firefall has staged content (see video for an elaborate explanation) which means that players need to work together to unlock a piece of an area. Once it is unlocked it is accessible for everyone.

Army (guild) feature is coming soon, trading isn't there yet but will come in the near future, open world PvP is expected to come in the second quarter of 2013. In Q1 they will start with the episodic campaign. By the way, Firefall is not a quest-driven game.
The community is nice in Firefall and the developers really listen to your feedback, they have a devtracker on their forums. The completely erased the leveling system (there was originally a level up system) and replaced it with tiers because of the feedback of the players.

There are four battleframes (classes): Assault, Biotech, Engineer, Dreadnaught and the Recon.
Biotech used to be the Medic, but the combination of the Medic and Dreadnaught was too powerful in PvP since it relied on the healing of the Medic. So Red5 made it sort of an attacking frame with healing abilities. A good choice by the way.

I play PvP mostly. It's crazy right now with the changed constraint system and imbalances but its doable.
Red5 is really into eSports so they are going to make eSports pvp maps. The game is a skill based shooter.
Currently there is Team Death Match (4 maps), Sabotage and Harvester. The last two are objective based modes.

Since it is free2play there is a cash shop in the game. Prices right now subject to change, some items cost absurdly high but its to collect data. They said they won't make this a pay2win game, so no weapons and all that stuff. Only cosmetic and convenience items.

 Screenshots

I'm having fun with this game.

EDIT: They are releasing the game this year making it accessible for everyone. I'm guessing in the summer.
I have one beta key left. If you give me your e-mail address, I'll send you it.