I've got a Dyson DC18 and it's been good as far as I can tell, but I haven't compared it with anything else. What did you replace it with? Is the replacement better? Did you try any side-by-side comparisons?
1. I've replaced it with a Miele and a Siemens (needed two)
2. The both clean better, I find less dirt in carpets and e.g. in corners than with the Dyson.
3. Personal subjective opinion: Having a bag is cleaner for me.