Maybe they look a little flat or dull and muted instead of vibrant and rich in colour depth.
I have said it before and I will say it again. Every photograph that you take in a digital format could use a little help afterwards in a photo editing package. The results whilst subtle can make all the difference.
You don't have to use software that costs hundreds of pounds either. Lightroom or photoshop elements are more than adequete.
If you have the ability to shoot in raw then I suggest that you do but you will have very dull results to start with.
Here is an image opened up in lightroom from a raw file.
In the basic adjustment tab we increase the clarity and vibrance a little and lower the tone curve to give the image more colour depth, contrast and generally improve the overall look of the image.
Whilst this takes little to no time to do the results really are worth the effort.
In a side by side comparison you can see the subtle differences (depending on the quality and calibration of your monitor) that a small investment of time can make.
(Please click on any of the images to enlarge them)