I believe people should be able to make informed decisions, so here's what we know about Star Citizen Alpha 3.0 so far:
Three moons (Yela, Daymar, Cellin) and an asteroid (Delamar) that you can land on.
A new station/outpost (Levski).
Cargo, salvage and trading.
New missions, two mission givers (Ruto and Eckhart).
Basic NPC AI (aka subsumption).
Breathing, stamina and heart rate simulation.
New ships and vehicles, major reworks for existing ones.
New RSI launcher with delta patcher.
No mention of the new netcode or player counts.
No mention of a new TOS.
Full patch notes:
https://pastebin.com/ns8vTSp4
Update 1: Comments from Evocati members
Launcher is 223 MB, full download is 38 GB
Moons are very pretty, landing is indeed seamless
Performance is poor, like 5-15 fps most of the time
High memory requirements, 32 GB RAM / 11 GB VRAM is a must
Lots of new bugs, in addition to the old 2.6.x stuff
Some questionable design decisions: poor visibility in some cockpits, MFDs can be used only with a mouse, UI in general is a mess