I’m curious about how folks like to handle variable screen dimensions in 2D games, particularly as it relates to game play and “fairness”. This goes for either changes in the window size or screen resolution, which is effectively the same.
Imagining that a game was designed for a standard 4:3 ratio, the following can be done when the user or game switches to another screen dimension:
(a) Lock the ratio at a fixed value: either keep the world view dimensions by scaling the view down to fit in the screen dimension, or locking the window size or screen resolution to a preferred ratio. The first one will create unused screen space on either the sides or top/bottom of the screen. I imagine this is almost necessary for games where the range of visibility is a critical factor in play.
(b) Use the extra screen space to give more world view. Depending on how the window is shaped, this can give either a vertical or horizontal view advantage to the player.
© Truncate the view either vertically or horizontally to match the minimum world dimension to the screen. This creates a player disadvantage for non-standard dimensions.
(d) Others?
What’s your preference? What kinds of games are most/least affected by this, and how? Do you let players who have large or wide-screen displays get their money’s worth ? 
(or folks who are willing to create a narrow wide window at the expense of detail). Do you fill dead space with pretty filler or leave it black?
I think varying ratios are less noticeable in 3D games, especially where changing the FOV is allowed – the player can trade off field-of-view for detail at will, and a little extra screen space on either side due to a funky resolution doesn’t seem to make much difference, though I’ve never played 3D on a true wide-screen – maybe I’m totally wrong.
-Pentalon