Funcom is showing the full game for the first time to players at the Leipzig Games Convention, without an NDA so videos are already showing up on Youtube and elsewhere. Here's a developer demonstration of siege weapons in use, simulating how players might lay waste to another guild's fortress. Towards the end of the video there's some additional good combat footage amongst the ruined chaos. I believe the class played is a Dark Templar if I'm not mistaken, at least I'm seeing some dark-looking magic debuff as others attack him.

Although there are stunning moments, it looks a bit strange with the accelerated building, super fast trebuchet launches and dozens of support NPCs standing around, the developers really should be more careful with their god-mode cheats which could give a wrong impression of the game. Still, you can watch this and see what they're trying to demonstrate and imagine a bit of what a largescale guild vs guild PvP siege battle might look like.

The same demonstration is repeated in another video at Stage6 (annoying browser plugin required unfortunately), where you can see how Funcom scripted the temporary siege event for the trade show.