I'll try and break down each SDK. GECK: Great for designing unique terrain and interiors and somewhat easy to import custom weapons and items. Dialog and creating unique characters is more of a challenge. Deus Ex: Yeah it's old, but the game is getting a huge revival of attention and support thanks to the success of Human Revolution and the release of a couple high-profile conversion mods. Not user-friendly though, and importing custom models is tricky (even the developers only used one character model for 80% of NPCs and just retextured it. Notice how many people wear long jackets with short hair?) Aurora: Hoo boy, I can tell you from experience that this engine can make writing dialog, creating complex characters and structuring missions a cinch, but if you don't want your game to use strict Dungeons & Dragons rules, you're in for an uphill battle. Almost every core gameplay mechanic is hard-coded and the system is very limiting when it comes to designing areas. Plus, the community behind the game is quickly and quietly fading away. REDkit: I haven't had a chance to try this one out yet, but knowing that ProjecktRED built the first Witcher game off the Aurora engine, it may have some similarities. All these engines have pros and cons to your project. If you're more concerned about story with gameplay, Aurora can help you tell it easily, and the D20 Modern content packs will give you almost all the sci-fi content you need. If you think you can tackle a tougher system, then Deus Ex would be your better bet. The gameplay is much more flexible and already does dark and gritty sci-fi just fine. Hope this helps!
