THE GOOD
There's a lot good to be said about the beta. First off is that it already feels more finished than a lot of other games do at launch, so much kudos there.
Secondly all the decisions and additions to Rebellion, as far as I can tell given the scope of the beta, have paid off. Titans are rather excellent, and beyond how fantastic the models look, I must congratulate the sound and VFX teams for giving them an awesome presence. Their very existence is a Psychological Weapon of Mass Destruction, the rich sounds and vibrant explosions that radiate out from these monsters is awe inspiring. Even a Titan I own gives me the heebie jeebies. Corvettes are welcome as well, filling a nice little niche that I didn't even know was there.
The graphics are superb and even later in the game I notice little performance impedance on my relatively RAM and Processor challenged machine.
New victory conditions are fun (especially awesome is combining Flagship and Occupation victory, I recommend if you've not yet done so).
I like how killing the pirates is now open to everyone. Previously you had to be, or had to have on your team, a TEC player capable of building a Novalith cannon if you wanted to destroy their base without committing (and losing a large portion of) your fleet. Now with Titans, everyone can have a go.
THE COULD BE BETTER (this will have to substitute for a "THE BAD" section, as I don't think this stuff is bad per sé)
Speaking of the Occupation Victory, the neutral fleet around the victory planet is a bit....weak. Even though there's a Titan there I don't really feel there's any need to bring my own. An early to mid game fleet can handle the garrison quite nicely with minimal loss. I suggest a beefing up all round, stronger Titan, fully armed and operational starbase and a better fleet, to add challenge to taking the planet in the first place. Either that, or at least make it tweakable in the game settings how well defended it is.
Final note on the Occupation Planet. It seems to have a higher incidence of Space Ponies than most others. I and some other players have discovered our first space ponies there, and I have since gone on to find Space Ponies on other Occupation planets as well. Maybe this is intended I don't know, perhaps Space Ponies are the secret ingredient to Galactic Domination.
Also, if I set an AI team-mate to "Random", I can't seem to tell if they're Loyalist or Rebel until they build a Titan or Corvette, which they don't, perhaps an extra line under their name to clarify their faction? As this time the differences cannot be told cosmetically.
BUGS
Short list here, most of the ones I've noticed have been caught in the Known Issues thread.
First, the AI is bone idle with its flagship, if cornered, the Flagship will not attempt to flee and will not use its abilities until the last minute. An enemy flagship decided to try its luck against my Ragnarov and only used invulnerability when it was down to 500 hull. I didn't see any other ability getting used. I also feel that the AI in general is slightly less challenging. "Normal" AI's now don't seem to build fleets like they used to.
A graphical glitch with the Ragnarov, if firing at something parked right off is nose, the Gauss Guns on its arms will fire through the bow.
END
That's about it, hope you found that helpful.