Here is a direct comparison of specifications:
Here is a complete review of the Nikon J1 (& its more expensive brother V1):
I notice that the J1 does not have a viewfinder at all.
That can be a problem on a bright sunshine day.
It is also a problem when doing action photography and trying to track the action.
Years ago I used to take professional pictures for portraits, modeling (people just starting out needing comp cards and a portfolio), a few small weddings, landscapes and flowers. I stopped and just never really got back into photography. Now I have a son who I am always taking pictures of and some landscapes and vacations with a small compact digital camera that I really do not like but it was a gift so I used it. I just traded my Nikon F100, Nikon Nikkor AF 28-105mm, Nikon Nikkor AF 70-300mm ED and my SB-28 flash (they only gave me $150 for whole outfit) in for the Nikon J1 but I'm wondering if the D3100 would have been the better choice for me and if so I have time to return and do an exchange since it's only been 3 days not to mention I'm sorta feeling like I got jipped. I went into the store to look at the D3100 but was talked into the J1. I haven't had the chance to really play with it yet but will today. I'm not picky about having or not having a view finder or shoe for a flash, size, control options or really anything else except the image quality. I want sharp images that will enlarge (nothing bigger than 11x14) nicely and still be sharp. Everything else I can go either way and have no preference. I mostly e-mail and post my pictures but do occasionally print a few for family use. I can not afford anything more than what these two cameras cost so I do have a limit. I don't have to use Nikon and am open to other models and brands too. Thank you in advance for anyone's opinion.