There is not much more I can add to the reviews already posted here. Jelling is a small village and the mounds sit right in its centre. In between the two mounds are a church and the two stones. The church unfortunately was closed for a funeral so 10 minutes after arriving I had climbed the two mounds and looked at the stones and was left wondering what else I could do. Fortunately the free museum was open, and this was superb. It really explained the significance of the site, and also helped decipher the stones for me. There were castings of the stones that were painted in vivid colours, these helped reveal the details of the engravings and also highlight the narrative of the text. Without the museum this would have been a slightly dull site to visit, however the museum did a great job of explaining the significance of the monuments.
As said by the other posters here, Jelling is not the most astounding of sites to visit as the monuments are rather small, however the significance is well illustrated by the on site museum making this an interesting place to visit for a few hours.