We are taking my son in September and he'll be 3 1/2 by then. We took him last year in May when he was 2. What he enjoyed more than anything was riding "his" rides over and over again. We just let him and his sister (6 yo) pick out the rides they wanted to do (my DH and I didn't really care). We rode IASW ~30 times (not joking). In fact, every day we would end up back at MK just to ride IASW (quick, no line). We rode Peter Pan probably 5 times, the teacups and Dumbo about a dozen times each, the people mover, etc. We just let them do what they wanted.
The reason they were so into rides is because we met Mickey and the gang already on the first night at dinner - we ate at Chef Mickey's. I like to do that so we don't spend our time in the parks waiting in line to meet characters. The good thing about it first was that it got my DS used to the size of the characters. Goofy really startled him. But, by the end of the dinner he got the picture. I would recommend combining character M&Gs with meals whenever possible - 2 birds, one stone.
Okay - here's our other secret - and truthfully, I'm not sure if you still can do this because of the character switch-ups at AK. But, when we go to AK, the first thing we do is go to Camp Mickey and Minnie and wait for it to open. People probably think we're nuts standing there at the rope because they think there's nothing down there to do that early. But here's why we do it. If you go down there at 10 am (when that section opens), it's completely deserted... except for a bunch of characters. As you round the corner by the Lion King stage, you will literally see like 10 characters just waiting there for you and your kids. It is the most amazing thing for little ones - it is honestly just like the commercials. I don't know what characters are down there now, but when you get down there, ask a cast member if any more characters are coming out. If so, ask them if you can wait by the gate and help the character walk to their spot. My DD and DS did this with Chip and Dale last year and it was amazing - one of the best memories ever!