Looks like there's a new wave of online previews coming thanks to the recent Vegas press event. IGN has posted one of their own with some new info and screenshots. Here's a snippet:
There's lots of new firepower, for sure. But you'll need it when facing off against some of monsters that inhabit the area around New Vegas. As Obsidian has a history with the Fallout franchise, it is making sure that the longtime fans see things that make them get all nostalgic. New beasts like the mutant Bighorner are joined by some old foes. The Gecko (normal, Fire, and Golden variants) and the elite Super mutant Nightkin are back, the latter of which can switch on some active camo to make things extra tricky. While the Nightkin is invisible, you won't be able to target them in VATS.
Things get trickier yet when you add in the new armored defense some elite enemies can present. When targeting some of the stronger units in New Vegas, you might see a red shield appear on the screen. That would be your indication to switch weapons to something more effective. Perhaps a Plasma caster would be called for.”