I just imported a PowerPoint file (on Mac so the conversion is done by Keynote) as images, and was shocked at the quality.
I found Keynote is exporting at 960x540 pixels, and there seems no way change that.
I have done the import via Keynote previously and not noticed any issues. Has Keynote been crippled recently, or have I just been unaware?
Fortunately I was able to export the slides from PowerPoint, and could specify the desired resolution.