Nothing is wrong with your settings. Mathematica 10 is supposed to be using the old fonts. The old fonts are shown in the blog post introducing Mathematica 10.

But you can play with the new fonts if you like. Go to Format -> Edit Stylesheet.... Create a new cell in the style definitions window. Show the cell expression by selecting the cell bracket and pressing Command-Shift-E. Then change the cell expression to

Cell[StyleData["StandardForm"], FontFamily -> "MathematicaSans", FontSize -> 12]

convert the cell back (Command-Shift-E), then close the style definitions window. Now the notebook will use Mathematica Sans for standard form expressions.

Here's a better example showing actual code:

You can also try Mathematica (serif) or MathematicaMono (fixed width). The fonts are located in $InstallationDirectory/SystemFiles/Fonts.

Nothing is wrong with your settings. Mathematica 10 is supposed to be using the old fonts. The old fonts are shown in the blog post introducing Mathematica 10.

Note: People report that the hack described below doesn't work on Windows or Linux. It works on OS X, where I tried it.

But you can play with the new fonts if you like. Go to Format -> Edit Stylesheet.... Create a new cell in the style definitions window. Show the cell expression by selecting the cell bracket and pressing Command-Shift-E. Then change the cell expression to

Cell[StyleData["StandardForm"], FontFamily -> "MathematicaSans", FontSize -> 12]

convert the cell back (Command-Shift-E), then close the style definitions window. Now the notebook will use Mathematica Sans for standard form expressions.

Here's a better example showing actual code:

You can also try Mathematica (serif) or MathematicaMono (fixed width). The fonts are located in $InstallationDirectory/SystemFiles/Fonts.

Nothing is wrong with your settings. Mathematica 10 is supposed to be using the old fonts. The old fonts are shown in the blog post introducing Mathematica 10.

But you can play with the new fonts if you like. Go to Format -> Edit Stylesheet.... Create a new cell in the style definitions window. Show the cell expression by selecting the cell bracket and pressing Command-Shift-E. Then change the cell expression to

Cell[StyleData["StandardForm"], FontFamily -> "MathematicaSans"]

convert the cell back (Command-Shift-E), then close the style definitions window. Now the notebook will use Mathematica Sans for standard form expressions.

You can also try Mathematica (serif) or MathematicaMono (fixed width). The fonts are located in $InstallationDirectory/SystemFiles/Fonts.

Nothing is wrong with your settings. Mathematica 10 is supposed to be using the old fonts. The old fonts are shown in the blog post introducing Mathematica 10.

But you can play with the new fonts if you like. Go to Format -> Edit Stylesheet.... Create a new cell in the style definitions window. Show the cell expression by selecting the cell bracket and pressing Command-Shift-E. Then change the cell expression to

Cell[StyleData["StandardForm"], FontFamily -> "MathematicaSans", FontSize -> 12]

convert the cell back (Command-Shift-E), then close the style definitions window. Now the notebook will use Mathematica Sans for standard form expressions.

Here's a better example showing actual code:

You can also try Mathematica (serif) or MathematicaMono (fixed width). The fonts are located in $InstallationDirectory/SystemFiles/Fonts.