I've talked about inspiration before, it can come from anywhere and everywhere in all manner of contexts. At one point I even saw the face of a turian in my shower curtain which lead me to believe it's possible that's where the guys from mass effect came up with the idea. The important thing is being able to recognize inspiration when it comes to you and being able to use it accordingly. For now I'm discussing a popular form of inspiration in which we look for it in places we know it exists, such as similar forms of media that we're aiming for. A painter may look at other paintings from other artists to try and find their inspiration or to find a new one based on theirs or somehow connected. Directors may watch movies, just as writers will read books. Thus game developers will likely play other video games and see what they like in the game and try to understand what idea the concept stems from, what the source of it was and the steps taken to get to it. In effect it's a slight step below reverse engineering.
I recently talked about the core emotion of a game. The emotion however is not usually what the game is centered around, however it's in the first circle of primary things that all subsequent arms of the game are developed on. The very central core idea is a very specific concept a genesis point if you will. While the story of dante and thus likely the game are based on love it's usually not so straight forward. For example while I sit here drinking some root beer and thinking how long it'd been since I hat a float I find myself designing a random game that's seemingly unrelated and yet somehow it fits perfectly. It's an epic adventure of a hero in search of treasure. He'd seen it once before as a child and has been consumed by it ever since. He is determined to find it yet his desire has made him lost in a foreign land. He must make allies and fight the defenders of the treasure. You can see how the idea could then spiral off into specific abilities or skills, it would likely be an RPG, and in the end you'd probably get the treasure, and since it's me who's making it I'd probably make it some kind of golden milkshake or something. I'd probably have that in there somewhere at least even if it wasn't the final treasure. The core emotion of the game would probably be lust, which would be an interesting idea to play on as other side quests and NPC's try to steal your desire and make you quit your quest for the treasure. Of course it could always be re-written so that you're defending the treasure or avenging your family who was killed over it, any number of ways, but you'd see that in all of them my root beer float has become this treasure and the whole game is about getting it in some manner. I'd likely get you to empathize with the character though a sad story of how much he's sacrificed for what he wants and what he's lost as a byproduct, inflecting that all he really wants is to be happy and that the only way that can happen is to get the treasure. Cue violins. Then the sequel would be a perversion of the concept likely he'd have to sacrifice the treasure to save the world or something and it would suck and that's why it would fail.
What happens most often with games that fail is that they lose sight of what the game was really about to begin with, this includes sequels. Though in fairness complex sources of inspiration are easy to lose sight of, making it all the more important to clearly convey thoughts and ideas early on so the source can never be lost. This is because the core ideas are so clearly tied to the source and it lives on in every facet of the game from that point that even if it were cut out you could tell from the pieces around it what it should be. I'll remind you that everything can be an inspiration if you look for it, this even includes the search for inspiration being an inspiration in itself.