EVE:Online is a single shard, zero instancing MMORPG. This means everyone is in the same 'universe' interacting with one another. It means that when you are quietly PvEing someone can find you, interupt you and if you in a low security system... kill you or help you... most likley kill though. Not being prepared for this is considered your own damn stupid fault.
Smack talk is frowned upon. Smack enough and people will just kill you out of pricipal.
The universe is split in to solar systems, each has a security rating. 1.0 being 'safe' and 0.0 being 'free for all'. Not that you are safe anywhere in EVE. If someone wants to kill you badly enough, they will find a way. Security drops in 0.1 incriments so you get 0.9,0.8 and so on systems which affects the PvE rats that spawn in asteroid belts and the quality of those belts (along with mission rewards). Generally speaking people will leave you along down to 0.5 space as after that CONCORD (NPC police force) will not respond.
Unlike other RPG's where continual play is required to 'level up' EVE has gone for a time based system, you purchase a skill book from the market and train that skill. Each still has 5 levels and a time multiplier.(1x, 2x and so on) with is applied to your characters stats. Skills continue to train when logged off, but require an active trial/paid account. An item or ship will probably require multiple skills to be at certain levels before you can use it.
Ships come in various sizes: Frigate (your starting ship is a frigate), Destroyer (universally considered crap for combat), Cruiser, Battlecruiser, Battleship and capitol ships (Dreadnaught, Carrier, Mothership, Titan) although capitol ships are specialised units not OMGWTFPWND mobiles. A lot of ships have Tech 2 variants such as Heavy Assault Cruisers, Maruders, Interdictors and so on. Again highly specialised, but quite fun
You also have structures players can errect, things you can research, build, sell. It is worth noting that the economy is 100% player driven. You can be ripped off if you don't pay attention... you can rip people off.
Basically, all the crap players usually can't get up to (manupulate, decieve, back stab, greif) in other MMO's EVE allows, encourages and supports. It's a cruel universe and pod pilots (i.e. players) are very cruel immortal demigods.
And yes, it IS as bad ass as it looks. I highly recommend people who are looking for a decent space MMO or even Elite 4 to give a trial account a whirl.