Its incomplete. Its buggy. There are no Terror Stars til tomorrow; they will be buggy. There are only 6 (tomorrow 7) races. There is a list of bugs that have been reported but not fixed yet as long as your forearm (was as long as your leg - some more will get killed tomorrow but not everything on the Reported list). There is no Metaverse option. Not sure if the espionage system is working yet, possibly deliberately off.
In short, it is very much a working beta (in both interpretations of the word.) If you have held off this long because you were not interested in participating in, dealing with, contributing to beta tweaking, and didn't want to be frustrated by occasional crashes, save games that won't roll over to the next tweaked version, developing favorite new tactics/strategies that turn out to rely a 'feature' that gets cut, then you should continue to stay away. You might want to just do some game starts look at the new graphics, check out the tech trees, etc, without committing to a long game.
If you don't get bent about little stuff like occasional invisible ships, or planets that don't produce quite to the numbers they are supposed to; if an incomplete but 'adventurous' experience seems better to you that 2 more months of waiting, then try it. Especially try it if you have the patience and clarity to stop play, even to deliberately end game, and calmly write up flaws for the devs to track down. That is, after all, the real reason this 'pre-TA' product is out there. Just keep in mind that the one that you own, the item you purchased with certain expectations of quality, will not really exist until sometime in January.
If you do start playing, I recommend that you read the devs Reported Bugs update, and maybe the 8-10 top posts in the Beta Reports forum, every day before you start cranking turns.
drrider