... there is one truism that augurs well for publishing: Great marketing is no longer enough – if your product, be that a book, game or other storytelling project, is substandard, you will be found out, and the days of getting by on reputation alone are numbered. Basically, make a great game/book/product, and build your marketing with confidence from that point.
On the other hand, I no longer believe you can expect a great thing to accrue its own marketing on its own. The magic word-of-mouth we all like to assume exists, the kind where the stone you nudged downhill with your toe turns into a landslide, is as much a product of sheer luck and network effects as it is effort.
That said, I suspect there are very good reasons why those things are a product of sheer luck and network effects. In other words, the code can be cracked if we're diligent, but I suspect it requires access to the kind of metrics and stats that most self-published authors are either not in the habit of harvesting or simply don't have access to.
The fact that each self-publishing platform is an island unto itself doesn't help — it's next to impossible to harvest data from them, since they don't publish it. Maybe a sort of coalition of performance data sharing between self-publishers could be created — a way for individuals to tap into the collective data created by so many people working solo, side by side.