Yeah, that's always the first question... a cheap filter on the lens can cause soft images.
Next thing to consider is shutter speed... BTW if/when you post try to keep EXIF intact (some image processing softwares remove it if you "save for the web"). Too slow a shutter speed can allow camera shake blur... even the vibration of the mirror and shutter can cause blur at certain speeds. Image Stabilization might help, if your lens has it. But even it has a limit.
Subject movement is the other reasons for soft images.... too slow a shutter, once again. IS can't help with subject movement.
Missed focus is another possibility. Could be the focusing method being used or the mode chosen (One Shot for moving subjects would cause problems... AI Servo can't be used for a focus and recompose method... etc.).
Or it could simply be that you are coming from a much lower resolution camera and in the habit of looking at images at 100% on your computer. With an 18MP camera, that's like making a five foot wide print from the image, then viewing it from about 18 inches. Sort of like walking up to a few inches from an old masters painting and wondering why all you see are brush strokes.
Also, it can depend upon the software you are using and your general work flow. If shooting RAW and not using Canon's software, any sharpening settings in the camera very likely won't be applied, so you need to sharpen the image again.
Computer monitors vary in quality a lot, too. The best way to check sharpness and everything else is to make a print on smooth, matte paper with a good quality printer.
The LCD screen on the back of the camera is not useful for critical evaluation of images. It's just not high enough resolution. Even zoomed in, you can only do a rough check of focus accuracy... and use the histogram to check exposure.
It actually could be something wrong with the camera.