You
definatly need to read some of the earlier pages.
And quite frankly, if I was going to use a premade engine, it WOULD NOT BE THE HALFLIFE SERIES.
Halflife was based on the Quake2 engine. And I have access to the Quake2 source. So I would just use that. Plus, it's nearly 10 years old so forget it.
HalfLife two is a first person shooter and this game is not.
Plus, it'd take just as long to read through someone elses work and make it work the way I wanted it to than to simply program my own engine. Besides, I have a few friends that are also programmers that will help with several of the engine components (e.g., networking, sound, etc.) so I'm pretty much focusing on the basic game logic.
As far as the rendering engine is concerned, I would rather use a highly optimized current rendering engine than something that's already 2 years old. The graphics component is done so I don't have to worry about that. I just have to create the necessary interfaces to supply the Refresh engine with what to go do with itself.
Plus, I wanted to program a 3D game with other people as part of a team rather than solo this time and OP3 was perfect for me.
Besides, the refresh engine is really good. Take a look at
http://genesis.outpostuniverse.net and view the Images section. THere are a few screenshots from the game there.
Also, for larger images (I think I left larger images), view page like 3 or 4 or something. They're around there somewhere.