I logged on to the test server to try out the Rikti content and holy shit, its nuts!
If you're in a zone thats under attack you CAN NOT stand still. You *have* to fight.
I teamed with some randoms and went from zone to zone waiting for attacks ... here be screencaps:
My first Rikti fight in St. Martial. I was running around when the call came that the Rikti were on their way. They dropped these crazy Elite Boss bombs first to clear combatants out. About 2 or 3 minutes later they ported in troops and drones. The bigger your party, the more troops were on your ass. Here its just me and one guy -- we had continuous waves of 10 to 15 Rikti at a time. They eventually overwhelmed us with Mentalists. We were able to hold them off for a little while though.

Once you and everyone fighting with you dies, the Rikti raiders port out:

You can see in this cap that we had a team of 4. We were trying to hold off the first wave in an attack on Nerva but were immediately overwhelmed by 12 mentalists and chief mentalists. Totally nucking futs!
And heres a fight in Grandville. As you can see, AoEs come in very very handy:

The upside is that most of the attacking Rikti are on your level or a little above you. Its never an unfair fight, it just gets intense very quickly. You also get a crapload of insp drops, so as long as the greens and reds keep dropping you can hold them off ... but its a whole lot easier if you have other people backing you up.
Its really fun to see the sky turn green and to watch the ground shake as the bombs fall.
I spent a little bit of time in the Vanguard DOP zone. Its structured a lot like the university -- you run missions to learn -- and the more missions you complete the more pieces of the Vanguard costume you can collect.
Can't wait to see all this stuff live!
