I went through this with my son and I found as he got older the rocking seemed to stimulate and keep him awake rather than make him drowsy.
The technique that worked for me is: To wean him off the rocking, each night I would rock him less and less before putting him down until eventually I was just holding him and not rocking at all. (example: still hold him for ten minutes but only rock for five of them and then just hold him for the other five) Then I was just holding, no rocking, him for five minutes at the most(this is important, no more than five minutes) and then would put him in his crib. Now if your son is used to being rocked for a long period of time he will most likely get upset when you stop doing this. Of course my son started throwing a fit when he wasnt getting his usual rocking time so I had to let him cry. If he cried for more than say ten minutes I would go in, tell him it is time to sleep, and gently lay him back down and leave. I went in at five, ten, fifteen, etc intervals and did this consistently until he was asleep. (make sure you do no other talking, just 'its time to nap' or 'its time to go to sleep') Eventually we replaced book time with the cuddle time and my son goes right to sleep! I found when I stopped the rocking he stopped needing/wanting it. Now he is like if you arent going to rock me then just put me in the bed. Yeh!
Make sure you are having smooth transitions also, this helps a lot and of course the consistent rituals-bath, book, bed or whatever yours may be. You cant really control the playing in the crib except by limiting the number of toys. Also I realized as my son got older he needed more physical activity to get him good and tired for his nap. Hope this helps!