You have power commercial developers don't: You don't have to worry about the commercial viability of new gameplay styles. Commercial developers have to worry about appealing to retail, breaking even, and other nasty things, which is why most games are slight modifications on already proven gameplay. But you don't. You can try out truly new gameplay ideas that just might become the Next Big Thin..
You have another power over commercial developers. You can release much, much faster and more often than they can. We've summarized this mod development philosophy with the phrase, "Release soon, Release often." Commercial developers work for 2-3 years, release their game, and hope to god people like it. You don't have to make that leap of faith. You can design your whole mod, write 25% of it an..
Create realistic goals for yourself. Think about how long it takes a commercial developer to make an FPS shooter with 10 weapons. If your mod is going to have 40 weapons, you're making life really hard for yourself. The thing to keep in mind here is "Quality over Quantity." Players would far prefer to have 10 unique, well balanced, and fun to use weapons than 40 unbalanced weapons, some of which..
When thinking about your game design, don't fall into the trap of believing that "Different is Better." There's no reason to rewrite the shotgun code and have a new shotgun model if it doesn't impact your game in any interesting way. Keep in mind the first question, "Why should someone play my mod?" The answer, "My mod has a new combat system, and a new movement system," isn't necessarily a good..