Let's see, where to start...
First off, the similarities are more to Privateer/RF and Priv2, though there's work on the next patch to put more of an emphasis on military factionalism (3 factions that the players can choose, 2 NPC factions). There is no specific plot to follow, although the GMs (Game Masters; Netdevil employees or contractors that are The Law, as far as gameplay goes) will work with players to create plot arcs (for lack of a better term, off the top of my head) that will advance the state of the universe. You can run missions for credits and experience points that will allow you to buy better equipment and different ships once you gain enough of both, though don't confuse experience points with the XP of more traditional MMORPGs like UO, EQ, etc. If you have someone buy you a piece of equipment for which you haven't the rank (level of experience, effectively), you can actually use the equipment, but it's not insured if you die with it equipped; certain ship types, on the other hand, become available only after you reach a certain level (and may not be available at all stations within your "home" faction; you can't pick up new ships in other factions' stations), and there's no way to work around that. Also, that you may be many levels behind another pilot doesn't automatically mean that they're better than you, or that if you go into combat with them they'll automagically win. Success in JG is almost entirely in the hands of player skills, not random dice rolls like just about every other MMORPG out there today. An awesome pilot in a mediocre ship can down a complete clutz flying God's Own Fighter, even if GOF is dozens of levels ahead of what you can acquire.
There's a wide range of commodities to trade from one station to another. Most of the base commodities are from the efforts of other players, mining six different types of asteroids, and the more advanced commodities are made by the stations using those mined raw materials.
Your ship (and each faction has 16 different ships to choose from, from the starting shuttle to dedicated fighter-type craft to freighters whose top speed isn't all that high, but has a rather significant cargo capacity and thrust to make hauling heavy loads not take all day) has mounting slots that allow up to a certain size of equipment (not unlike Privateer not allowing you to mount a shield5 on a Tarsus, for example) to be mounted, with several different considerations. Do you want a lighter-weight gun capacitor for better acceleration at the expense of total storage? A shield whose overall raw damage absorption is low but has a fast recharge? An engine that doesn't consume as much energy, at the expense of a lower thrust output? Those are just some examples of the decisions one can make when outfitting their ship, within the limits of having the equipment available (there are production stations for most equipment, and not all stations produce all equipment; the non-native equipment is there from being hauled in by another player).
As for the gameplay, the physics aren't "airplanes in space" like WC/SW games, but aren't pure newtonian like Independence War, either. There is a "gravitic drag" acting on a mostly newtonian model to limit speeds, to help gameplay (anyone brand new to IW who, without using the computer's help, has gotten up to a significant faction of C on conventional thrusters and then decides to stop probably knows what I mean). Acceleration is a matter of ship's mass (and the mass of its cargo/equipment) and the thrust of its engines. If you stop thrusting, you'll eventually drift to a stop, but if you're heavy, it will probably be a long time before you do so. The physics model does allow for the "afterburner slide" long-time WC vets are familiar with, as well as a somewhat limited autoslide equivalent (limited by that slowing when not thrusting in the direction of travel I mentioned, above).
Space is divided into sectors, with travel between those sectors accomplished by jumpgates (hence the game's name), which act not unlike WC's jump points in general function. In the fictional universe, one could theoretically travel between sectors via normal flying, but it'd take a long time. Gameplay coding, though, limits the sectors to being individual "rooms", with the jumpgates acting like "doors" between them; each "room" is something on the order of several billion meters or so on each axis, though most of the stuff happens within a few hundred thousand meters of the center of the sector, primarily for the sake of convenience to the players.
Right now, JG development resources are somewhat limited, due to the small active playerbase, but the head developer is One Of Us(tm), and a former player from the beta period. With the help of a small group of active players (of which I'm one, for the record) new functionality and equipment balancing is an ongoing process.
That's all I can think of for now, so if you have any questions, feel free to ask.