The upper two windows don't make sense to me, how do they open like that?

I feel the reflections are overdone, the windows look striped rather than reflective/glassy. It also looks like you have shadows cast on the reflections, making them darker, which isn't how reflections work at all. Plus, glass is transparent, so it doesn't really get shadows cast on it - instead, objects just block reflections. Try drawing the window without any of the highlights first, and then adding reflections of generic objects likely to be reflected in the window based on how you'll be using these windows, such as other buildings or tops of trees, or clouds. If there are big bright highlights, they'd likely follow the shapes of the imperfections in the glass, or be very large and few in number.

On a similar note, the bright blue colour of the windows feels very cartoony. Are the rooms inside bright blue? Is it meant to be the reflected sky? Take a look at real windows for inspiration and reference, as otherwise it's easy to lose yourself drawing symbols of things instead of what those things actually look like.

The open windows don't immediately read as being open, because the colour of the open areas is the same as the glass - bright blue. From the outside, the interiors of buildings usually look quite dark, so I recommend making the open parts dark.

Lastly, in the bottom window, shouldn't the frame of the upper section of the window be visible through the raised section? Or is the glass opaque?


Edit: Tried to do some edits for you:

The top group is just reducing the contrast in your highlights, adding darkness where there's no glass, and replacing the shadows on the glass with areas where the highlights are broken.
I also added the window frame in the bottom window in this and the other edits.

The middle group has no highlights or reflections on the glass (except on the broken shards), this is probably the most realistic scenario for windows viewed at eye-level (as opposed to from below or from above) but doesn't look very interesting.

The bottom group adds reflections of the environment - the sky and trees/buildings.

Have you considered making the windows transparent, so that the space on the other side could be seen? It'd avoid the issue with weird-looking glass, and be a nice detail for players. In programming this, the "trick" would be to replace the wall underneath with a section that has a window-hole in it.

Your new edits make the glass look a bit pillow-like rather than flat. You're on the right track though. Perhaps, try going for a larger "circle" of light, one that doesn't fit in the window. Also, remember that all the glass pieces are more or less straight and parallel, meaning you can treat them all as a single plane rather than a bunch of separate bumps.

In this edit I also warmed up the blue, but made it more grey rather than brown, as brown doesn't really read as glass to me.

To avoid the window looking like it's lying on the ground, show its depth:


Partial transparency would be a good idea, I agree. You could do reflections, or even just add a bluish-greenish solid area for the glass.