Mhmm, I'm not able to reproduce the issue on the vertical scroll images where you can't advance with clicking. No idea what could get stuck. That's bothering me . When I wait till it auto scrolled to the top and then use the "scroll-bar" in the bottom right or using the scroll wheel in the image or using mouse drag in the image to scroll up and down in the image I have no lags at all and can advance any way I like, left ctrl, right ctrl, mouse click, space.Thank you for the detailed reply dev...kudos to you for that and much appreciated. I understand what you are saying about building your framework and I don't think you should migrate to Ren'Py if you don't want to. N engine is perfect and you seem to know what you want to achieve with this one. Go for it!
As far as the vertical scroll images are concerned...the game auto scrolls once then stops. The player (me) can use the image to redo the scroll or view different parts of the body if you wish. After this is done the game 'sticks'. Mouse clicks will not advance the dialogue. (And "enter" did work for me in advancing dialogue.) As I said, it does not freeze, since I can go back and scroll over the body again...but that's all I can do until the engine sorts itself out...hence my first comment that it is slow.
I mostly play Ren'Py and all of them are faster than this.
As far as the renders are concerned, it is something I have noticed on the Unity games I have played, thus I assumed it had to do with the display code itself. In the game, Pia's eyes looked like she walked through some nettles that left a network of red scars. And the other girl (can't remember her name)...the freckles were too prominent, bordering on being discoloured. I have seen similar patches of discolouration in other Unity games, but never in Ren'Py games, which lead to my comment.
And a suggestion, currently you have three/four ways to navigate the ship and they overlap (map, clickable zones, train, and side bar). This could get a bit confusing. Maybe remove one?
Regarding advancing with "enter". You are right! But this isn't intentionally. The "hidden" button/trigger that advances dialog when clicking with mouse stays selecting doing this once and then you can keep triggering the button with "enter". Not sure if this could cause any cross-problems. Need to think about it and evaluate that.
About the images. No, Unity just renders the images out as Renpy it does. It's just my art style. The "red scares" in Pia's face is just make-up. I liked it, fitted the sci-fi theme and her wild attitude in my opinion. I guess Selene's freckles are a bit to prominent. I probably will reduce them a bit in the upcoming updates.
Regarding navigation. I want to keep the clickable zones. It should feel like you are able to roam around the ship by going from room to room. This would include the trains and elevators. The map is for overview and fast travel. I will improve the map in the future. Not sure if already in the next update or a later one. At least I hope it will be an improvement.
The quick navigation will contain mini images for characters and quests in the future. If you see a icon on the quick navigation you maybe would click directly on it, rather than navigating there by the clickable areas to save some time.
I know some people like clicking there way to other locations and others use quick navigation or map to go there directly.
You could argue the train wouldn't be necessary. But, the train is faster then walking and maybe there is a quest or an event in the future where time matters . Ingame time, no countdown timer or something like that. The most location changes cost time, usually a few minutes between bigger locations. Using the map or quick-navigation calculates the fastest path.
Personally I feel like every way to navigate servers their purpose.
However, I could add an option to hide the quick navigation completely, but I don't think it's too distracting when collapsed.