这个功能比较让人兴奋，传统来说，在二维软件中做三维效果比较痛苦，在三维软件中做二维效果也比较让人痛苦，特别是像flash，unity3d这类主攻交互的程序，在unity3d以前版本中，要实现二维的效果只能通过gui或者textures来做，如果要做一个纯二维的游戏那就很不方便了。
The upcoming Unity 3.0 will have a 2D Sprite Engine, as you can see from the press release:
http://www.gamasutra.com/view/news/27558/Unity_Announces_30_Platform_Support_For_PS3_iPad_And_Android.php

The press release makes it sound a little like the sprite engine is specific to the iPhone, but this is not the case.  You can see the “inside” info here (top secret):
http://forum.unity3d.com/viewtopic.php?t=47214

Creating 2D games is currently very clunky in Unity.  Basically, you have to billboard textures onto planes or boxes, etc.  There is no hit detection for pixels.

In case anyone misses the point, a 2D sprite engine makes Unity a one stop shop for game development.  This effectively provides competition to Flash and Silverlight, as well as the folks at Garage Games, and many others.

Being able to write games in 2D or 3D, and deploy to the PC, Mac, Xbox 360, Playstation, iPhone, Andriod, and Atari 2600… where do I sign up?