Ceiling – How to open this flush ceiling light to change the bulb

I am trying to open this flush ceiling light fixture to change a burned out bulb, but I can't figure out how to open it for the life of me.

It looks like this:

I am not sure what the brand or model of the light fixture is, but I was able to find a similar light fixture on this website (http://www.galaxy-lighting.com/item.aspx?item=24826), but there are only minimal installation instructions!

So far, I have tried unscrewing the screws around the base and then twisting counter-clockwise, pulling straight down, and wiggling it around. I tried using (what I thought was) some considerable force in all these actions, but it won't expose the light bulbs inside. At this point, I'm afraid of breaking it if I use too much strength.

Does anyone have any experience with this type of ceiling light fixture?

Update: I was able to take off the cover. It required a counter-clockwise twist after removing the screws. I had tried that, but it required a lot more force than I was comfortable using. It had guides along the glass cover to tighten the glass piece to the metal base, kind of like a lid on a jar. I think that after 6 years or so, it must have settled tightly into place, and when I was able to finally get it to twist, I actually ended up breaking the glass cover because it jerked open. I wasn't wearing gloves, but thankfully I didn't cut myself.

While I was at it, I changed the other ceiling light in my hallway and was able to take it off without too much trouble after "wiggling" the cover for a little bit before twisting it off. It also jerked out of place, but it didn't break. I took a picture of the cover, in case it helps someone else in the future.