Here's a quick copaste of the ol' Episode 1 requirements, first:
Valve wrote: Minimum: 1.2 GHz Processor, 256MB RAM, DirectX 7 level graphics card, Windows 2000/XP, Mouse, Keyboard, Internet Connection
Recommended: 2.4 GHz Processor, 512MB RAM, DirectX 9 level graphics card, Windows 2000/XP, Mouse, Keyboard, Internet Connection
Reaction does require at least Half-Life 2: Episode 1 to run, so keep that in mind. We were able to capture most of the prettiness that you see on the screens because our work box was actually a bootcamping Mac Pro. However, we aren't really pushing too much in terms of software so I don't think performance should be an issue to most of the ModDB community (if it is, let me know!)
We'll be distributing the game via an installer and a ZIP. In fact, I have just finished compiling the installer (using NIS); it's ~280mb. The bigger issue though is the uncompressed game requires ~650 megs!
That's way too big in my opinion, but I already know the major reason. Most of our textures are 1024x1024 or larger, and that instantly inflates the package. While it is a little late to be making mass resizes at the moment (particularly because it screws up the texture layouts/scaling on the map, blech), we will definitely look to change up the packaging after the initial release so that it is more user-friendly and pocket-sized at that.
If anyone in the community has suggestions on how to handle that in an effective manner, please leave us a comment! Also, on release day we'll be opening up the forums so we can better handle bug tracking and suggestions!