I understand that it is only 2 parks. Is DL that small that you can do it all in 4 days? WDW is 4 parks and in 4 days you are just getting your feet wet.
It also depends a lot on the pace at which you take everything in, what kinds of crowds you are dealing with in the parks and what exactly is on your 'to do' list. I must say, in theory, 3 - 4 days sounds like plenty at DLR, and for many folks it is. Although, because my friends and I don't really do a commando-style of touring and just kind of take things one moment to the next, at our own pace, with a loose plan of action, we have easily been there for 3 nights and 3 full days before and missed a lot of things - or at least I have missed a lot of things - and I am not even certain that 4 days would have been enough for my agenda! Some people are fine with just going on certain rides, eating in a couple of places, looking in a couple of stores and then leaving, having had their fill of DLR for a good while. Some folks are fine with planning everything they are going to do, see, buy and eat day by day, and those are the ones who probably get more done! And then there are those who just play everything by ear and see where the day takes them.
So, again, even though 3-4 days is a good chunk of time, and if planned right, you should be able to do mostly everything, I do know that I have come home from trips of that length thinking, "How did I lose so much time? I still haven't gotten to do (
X, Y and Z)!" Between all the photos I would like to take, all the shops I would like to look in (not even to buy anything necessarily, but because sometimes you find cute hidden details in these shops), wandering around the DLR hotels and Downtown Disney, all the rides I would like to ride and all the rest time that is necessary mid-day each day to maintain stamina and energy, I never seem to have enough time to get it all done!!