Well, look all those nice posts
First: Yes HL 1 it's a old engine, and a lot of people knows that. So, why I created Am? I start mapping over 3 years ago, and Am only was a simple proyect. Now it's a really Big proyect and I just in finish it.
Like some boy said, it's possible to change the same (and best) Mod, using HL 2's engine. I know, and it's easier too, because I don't need to code all new effects, add physics engine, shader effects and more, so what's the point? I started Arrange Mode in a simple HL engine, and I will finish it in the same HL engine.
One more thing: I really don't know if I will use HL2 content. I doesn't need it at all. But keep in mind it, those effects, enemies, shaders and more, could be make it in HL's engine. It's a very powerfull engine and I love it.
Talking about HL2 mods... Some of them really sucks. They just keep in mind all features from this engine and they didn't make any new effect. Its not the same pleasure, play a HL1 Mod, a mod whit a lot of work, and a HL2 Mod, whit the original effects, and new weapons or gameplay style? C?mon, this is not a challenge for any Modder.
Right, I gotta go, Gabe Newell is calling me