Depends what you’re looking for. The Hero3 is great for action sports to every day filming. Yet it is limited in a lot of aspects, say depth of field or manual control over aperture, audio levels, etc…but for what it is, the size of two matchboxes…it’s amazing!
I love it because I can literally carry it in my pocket or backpack and whip it out anytime, rain or shine. Plus it’s light and I can mount it on crazy things like this GIANT pole (filmed with the hd hero2)…so really it depends what you’re going for. I’ll always use my DSLR, my HERO3 will never replace it, yet it will add to the production quality of my films.