The scans might not look good because the scanner isn't configured properly. My advice is to use the below settings for your scanner and then attempt to scan again:
"Slide in holder, emulsion (dull) side up
Professional Mode
Current Setting
Document Type: Film [with Film Holder]
Film Type: Positive Film
Image Type: 48-bit Color
Resolution: 2400 DPI
Target Size: Original
Adjustments: Auto Exposure (first button) Selected
Unsharp Mask: Off
Grain Reduction: Off
Color Restoration: Off
Backlight Correction: Off
Digital ICE: On...Quality Mode
Scanned to TIFF" - *Source: Pentax Forums*
You might want to lower the DPI a bit, to decrease the scanning time.
