I've been playing this since launch, it's sucked me in pretty thoroughly.
The game really nails the feeling of being in a spaceship better than anything else I've played. The visuals and sounds are extremely well designed to this end, down to little touches like windows frosting over if you turn off life support or instruments steaming if you spend too much time near a star. Flying in hyperspace, docking, fighting... everything is built to have excellent presence. Sound plays as big a part as visuals here: the audio in this game is terrific and makes me wish I had the speakers to do it justice.
The universe is a bit sparse on content: there's just not a huge variety of things to do and kinds of interactions you can have. The ones that are in place, though, are generally very solid and so far have held my interest just fine. I do hope that the game continues to develop more content, it needs it for long-term appeal. There's a lot of potential for emergent scenarios and adventure that just hasn't yet been tapped.
Despite being described as an "MMO" the game is essentially single player, even in the "open" online mode, and unless you go looking for them it's rare to see another player and rarer to actually interact with them. The co-op experience is currently weak but right at the top of Frontier's priority queue to fix.
The ship flight dynamics are semi-newtonian, with a soft speed limit that changes based on engine power and that can be temporarily broken by boosting (like Freespace). There's a "flight assist off" option that lets you do the usual glide&rotate manevers, with the additional wrinkle that it also disables rotational correction. This makes turning it off a tactical choice that usually costs you your ability to aim finely, making it best used in short bursts by most people. The other big notable thing about the flight model is the airplane-like constraints on turn rate that have nothing to do with newtonian physics at all: your ship yaws much slower than it pitches, and both pitch and yaw speed vary based on how fast your ship is moving (there's a sweet spot at about 50% throttle for maximum turn rate). This limit is shamelessly in place to promote a swoopy-chasey sort of dogfight over the mutual dodge&circlestrafe kind of fight you get with other 6DOF games like Descent & Star Citizen. It's not my favorite aspect but in the end it works well enough.
The UI is especially well done and elegant, giving you a ton of control over ship subsystems and modules while also being very easy to use. Power management is nicely essential to combat, even more so than in Freespace, and forces you to make real tradeoffs between defense, maneuverability, and firepower.
Overall, I think any space sim fan should pick it up and try it eventually... but I wouldn't blame anyone for wanting to wait for the price to come down or more breadth and depth of content to be added. Now if you'll excuse me, I need to go experiment with my Viper weapon configurations as I make my way towards Alliance space.