First of all, God commanded all of the males of the nation to be circumcised. Only Joshua and Caleb (the sole survivors of the exodus generation) had already been circumcised. So, at "the hill of foreskins" the whole nation ceased their activities for the rite of circumcision to be carried out. Circumcision was that intimate ritual that God had commanded as a symbol of the covenant that He had made with His people. It represented their faith in Him.
Secondly, for the first time, the nation celebrated the Passover Feast within the borders of their land. This was what their eyes had been set on since the day that they had heard Moses' promise of deliverance. They originally left Egypt to go and worship God. Finally, they were truly doing exactly what they had set out to do. They were worshiping where and how He wanted them to worship. It must have been a glorious occasion. They were finally worshipping God in remembrance of His mercy from a former time now ended.
The third new thing that wasn't new was the cessation of the heavenly manna. The very day after they celebrated that great Feast of the Passover, they began to eat from the food stuffs that they found in Canaan. With one day of overlap, God ceased giving them the free "what-is-it" bread that they had received 6 days a week for 40 years. He had a new program for sustaining them. It was a land flowing with milk and honey... manna was no longer necessary.
Finally, it also seems reasonable to assume that the cloud and pillar that had been leading them all along their way was no longer leading them (Exodus 40:38), after all, the last mention of it is in Deuteronomy 31:15 on the last day of Moses' ministry.