Buzzfeed was able to get these little bits of info regarding what to expect...
• Booster Gold reappears while an entire team disappears
• One team is trapped in a bottle while another is changed completely
• Some heroes change their colors and other change allegiances
• Pandora battles to the death
• A close encounter of The Dark Knight kind
• There's a new, old Creeper and some old New Gods.
• One hero quits, and another hero dies