When I first launched the game, it ran in full screen at high resolution and looked great. The second time I ran it, and every time thereafter, the resolution somehow blows up way past the screen size and I can only see the top left corner of the game and it is huge on my screen.

I have tried changing resolutions to see if it would bring the size down. It doesn't appear to have any effect. I can run the game in windowed mode, however in windowed mode some of the keyboard keys are sticky and it is very hard to play. Reload doesn't always work. Fire doesn't always work. And if I try to crouch and move at the same time, the guy just keeps running in that direction when you release the keys. This makes windowed mode unplayable also.

Is there any idea about what my problem might be and how to fix it? Or should I simply ask for a Steam refund?

The most frustrating part is that I know the game runs fine, because it did it the first time. I have even deleted the game and all its supporting content and started with a fresh install. For whatever reason, that didn't change anything, even when I deleted all the settings files prior to reinstall.

Hmm, haven't seen similar behavior on my Mac mini (OSX 10.9.5). Which OSX version do you have?

Can't really find similar sounding issues on Google; I'd guess you tried some other fullscreen games that they're behaving fine?

I am on the latest update of El Capitan.

Funny that you mention other full screen games. When I tried to play Crusader Kings II I had an issue with the bottom part of the screen getting cut off at first. I changed the resolution settings though and that problem fixed itself. I launched Civ V just to test it and it works fine in full screen.

With CKII, when I changed the game resolution I noticed a difference immediately in how the game looked on the next load. With RWR I don't notice a difference until I get down to the resolution that is like 1600x1050 or thereabouts. The game goes from full screen way too big to super tiny in the bottom left quadrant of my monitor.

This should be an album of full-screen screenshots at different resolutions for reference:

http://imgur.com/RIXF5OS&GK2rYLp&kn7lX0g&OGWslZV

Thanks, that gave some ideas although I'm still just guessing here. At least you seem to have some over full HD resolution display in play here, I haven't personally had a chance to try one of those on Mac how they behave. Generally RWR should be scalable, and if I'm not wrong, there are people who use those displays ok with RWR but I'd believe majority of them are on Windows.

To test some different configuration to get more clues, Is it possible to change the display resolution, like on the desktop, to a smaller one (close to 1920x1080 or less) and then try using the same resolution for fullscreen in RWR? Anything change by doing this?

I tried changing the resolution to various combinations, both up and down, and it didn't seem to make any noticeable difference. It seems that the game takes control of the display resolution at fullscreen, regardless of what the OS has it set to.

Also if you could give me some advice on how to fix the buggy controls in windowed mode, I would be satisfied just playing the game that way.

No such control issues in windowed mode on my Mac mini / 10.9.5 either. I believe I have installed SmoothMouse (www.smoothmouse.com) earlier, but sounds like the issues you had were more about the keyboard.

I haven't upgraded to 10.11 yet as I'm not sure how it affects my development environment for RWR, so it's anyone's guess if RWR is compatible with 10.11 right now.

I'd say at this point your safest choice is to use the refund.