What is actually being asked here? Things that make a game popular when it begins versus what maintains that popularity? These are difficult to answer.
Before writing a very long set of thoughts I want to point out that VERY FEW games really become popular before the third or fourth update (sometimes longer) as people want to see more than the basic content. Some developers give up on a project (good or bad) because they do not get 'enough' support after the initial release or even the first several updates. To be popular a Dev NEEDS to actually be willing to work at getting fans/support, and not expect people to flock to them for 5 minutes of content.
At the start Image quality and good writing are important as they draw interest. However, if a title has unpopular content (tags) it probably won't gain a large following. Of course, a game might not have the best images, and people might try (and LIKE) a game because the story sounds interesting. Honestly, I would have to say that to gain AND maintain popularity a game needs an interesting basic idea, good characters, HONEST tags, and relatively easy navigation and or quality of life.
To begin, the IDEA of the story/game needs to be good enough to interest people. A game needs to be different enough from all the others to draw people in. For example, a different type of main character, location, or setting could draw people to try something new.
To maintain popularity the ORIGINAL idea and Tags need to be followed. Sudden changes to the story (and tags) will damage the experience of players often to the point people will abandon a project they previously enjoyed. An example would be to add 'Surprise' content. This could be (but is NOT limited to):
1) NTR
2) RAPE
3) URINATION (water sports)
4) Hand holding and head patting
5) GRAPHIC VIOLENCE
If players have been warned before new content is added AND the story points to it appearing, the bad effect can be greatly reduced or even avoided completely. If two characters who have been enemies from the start suddenly begin holding hands and become the best of friends (and greatest lovers) without warning, then people WILL become upset as this new content does NOT fit and destroys the experience. HOWEVER, if people KNOW that these enemies will end up together AND the story (plus tags) show that the questionable Hand Holding is to be expected, then people will (generally) accept or even enjoy it.
This is getting too long so I will say that popularity is fickle. The BEST images are not enough to maintain popularity if the story is BAD. Also, many fun and popular games have been DESTROYED by adding a 'Surprise' that a developer hoped would bring in new fans.
I would have to say that what makes a game (or anything) popular is a mystery that will likely never really be solved. What makes something UNPOPULAR is easier (just look at modern day Hollywood).
Hope that helps.
