HTC seems to be going all-out with its quad-core smartphone portfolio. Just last week I reported on the HTC Edge. Unlike the Edge, though, the Zeta that you see above seems to be HTC's flagship phone for 2012.
While the Edge does indeed have a quad-core processor inside, it's only clocked at a (comparatively) measly 1.5GHz. The Zeta has the upper-hand in terms of CPU power: its quad-core processor is clocked at an insane 2.5GHz, a full GHz more than its little brother. The Zeta's other differentiator is the fact that it will ship with Ice Cream Sandwich, unlike the Edge.
But other than those key points, the Zeta will be, in most aspects, the same device. But really, the beast of a processor and the promise of Ice Cream Sandwich definitely makes the Zeta a better buy.
Hopefully, we'll see both phones sometime in the near future. My only concern with quad-core phones is the battery life, but by the time those processors are released, manufacturers should be packing bigger and better batteries to offset the thirst of quad-cores processors.
Update: The HTC Zeta is, unfortunately, just a concept.