You want me to take time away from playing Avorion to talk about Avorion? You monster!
I've had a chance to play roughly 16 hours so far, but much of that has been spent building my first space ship, a replica of the "Eureka Maru." It flies but its still not completely finished yet.
So I can't give you my opinion on much else. But I have throughly enjoyed it so far.
Do you like to build things? You have blocks, and slops, corner pieces, etc., along with engine, thruster, shield, power, hanger blocks, and others that you cobble together to create your ship. You get the resources through mining, with a mining lasers, or you can salvage it from recked ships. You can fly a giant cube if thats your fancy, or lose yourself for hours making a fairly detailed ship, its up to you. As you progress you will find better material to build or upgrade your ship with. You'll find new gear, turrets, and other weapons that drop from enemies that you can slap on your ship.
And if building ships, fighters, turrets, and stations, isn't your forte, there are tons of prebuilt things others have created and posted on the steam workshop ready to be used. You want to fly the Millennium Falcon, or the USS Enterprise, there are versions of them on the steam workshop for you to enjoy.
As for how well the game runs so far I haven't had any crashes, in two 8 hour playing sessions so seems fairly stable for a Mac beta of an early access. I've had one weird display bug in which the text for the settings menu disappeared. I haven't been able to replicate it since, if I do I'll send a bug report, after all thats kind of the point of this Mac beta. Thats been the only issues I've had so far. But there is a lot more of the game to explore so there might be more bugs.
If you want to get a feeling for the game there are a number of playthroughs on youtube that can give you more of an idea than my ramblings can.
Hope this helps.