I think there is a golden balance of sorts in polish and ambition. It applies to all parts of visual novels, but it's particularly easy to see in art.
I have made a picture to illustrate what I mean and will go on to explain it.

Effort, polish and ambition decrease to left and increase to the right. Behind the text and colours is the curve of enjoyment and quality.
At the far left are the creations that are created with an obvious lack of polish - the kind that make you wonder if the creator was thinking at all. Note that this isn't a measure of skill or quality, but effort and polish: even the best of artists or writers can fall into this section if they simply don't even try, while beginners don't automatically belong here. The productions and assets within this section usually disappoint the audience and do not demonstrate the potential of the creator, who may feel disappointed in their own work.
On the middle left is the "homey" section. I believe this is what you meant by "nice" games: you can see that the creator didn't intend the work to be their greatest masterpiece of all time, they just used the time and effort that they felt was neccessary. The creations in this section create cozy and pleasant feelings for the audience. They do their job, but they are nothing their creator would put in their portfolio or CV, as they feel they could do better. Because all of what the creator did was in their comfort zone, there are no real mistakes or so, but the product may leave people wishing for more.
The middle section, the golden balance, is what every creator should aim for: the part where the effort and ambition match the actual skill. These works are perfectly polished and show no strong weaknesses. In general, the results are what you would call good work, and realistic displays of what the creator is capable of.
But when we go to the right, and add more ambition and polish, the work gets "bumpy". An example of this would be that an artist who isn't that technically skilled trying to do realism or perspective drawing. While the work shows that extra effort was made, the ambitions and skill don't match, resulting in work that may be better in one way and worse in the other compared to the creator's average work. In a visual novel, this shows as uneven quality and lack of harmony.
And then there's the extreme right, which I'm sure all of us have seen. Some people may not introspect as much as they ideally should, and the result is that they think they can do more than what they're truly capable of. What happens here is a rapid decline in quality and the enjoyment of the audience, just like when they do the complete opposite. In large projects like visual novels, this can also often lead to the project never getting finished as the creator discovers that they overestimated their ability and cannot match the demands of their vision.
So what you should actually be looking for is a fine balance. Ask yourself what you are capable of and what amount of ambition will produce the best results, because both neglecting polish and aiming too high will make your visual novel worse than what it could have been should you have reached the golden balance. Looking for the balance is very difficult, one of the hardest things in making visual novels in my opinion, but also crucial and surely worth your time.
Personally, I feel like I'm still searching for my own balance, especially in writing. It's surprisingly difficult to set aims that are both realistic and satisfactory, but I think my image of what I can do is becoming more clear all the time.
EDIT: thanks for lordcloudx correcting me, I meant "homey" and not "homely". Doh!