That is the question. And the game in particular right now is Deus Ex. The question I am asking myself is "Is it worth it to invest so much time, energy, and resources into something that has already been done?" We would literally be remaking a hit game (just the first level actually)--from scratch--and hoping not to get foxed in the process. Just the thought of coding all those systems is scary.
The thing is that I could be spending these resources on creating something totally original. The only bad thing about being original is that you might suck. And coming up with good ideas isn't exactly easy. But I suppose the only way to find out if it is worth it is to lean into it and test the waters, and that is actually what we will do. If our prototype turns out to be the result of too much time to create something that isn't really that fun, then the project will be trashed in Cryptozoic-storage (no idea what that is, by the way :P), but if it is awesome, if it makes our blood rush, then we will move onwards. So here's to the prototype!
I recommend you make something original, but make sure to do a ton of planning and figure out the genre, engine, art style, setting, story, backstory, gameplay, etc first.