We took our DS for the first time this past May - he was 17mo & I'd do it all over again in a hearbeat
I heard from a lot of people who thought he was far too young to "understand" - but he LOVED, LOVED, LOVED the characters

The first time he saw Pooh Bear at Crystal Palace was the most adorable moment I've ever witnessed! Of course he won't remember any of it, but I know I'll never forget - the entire vacation was priceless. Sure, he had a few meltdowns, but he does at home too (actually he has more at home).
In any case, here's some more info that may (or may not) be helpful:
-We too brought DS stroller - although he REFUSED to sit in it! Believe it or not, that little guy walked ALL OVER WDW!!! Also, be sure to have a rain cover for your stroller.
-We also went back to our resort each afternoon for DS to nap. He really needed it after all that walking, besides he's never napped in his stroller
-Do character meals - DS LOVED the characters and the meals gave him the chance to enjoy them without us having to wait in excruciatingly long lines to meet them. Characters were easily the thing DS enjoyed most on the trip - he thought they were GIANT stuffed animals (gave them hugs and kisses

)
-DS loved MK best, he also enjoyed a lot of the rides at Epcot (more than we thought he would). Basically, we took him on almost every ride that didn't have a height restriction - I was nervous about him riding pirates but my nephew insisted we must give it a try. I was shocked that he liked it! I must admit though that DS seems to lack any sort of fear - he's a thrill-seeker in the making (much to my dismay).
-If you're flying, don't do a night flight! I can't stress that enough - by far the only bad decision we made about the whole trip. Between DS and the tot behind us, there was at least one baby screaming the entire 3 hour flight
I hope this info helps, if you have any questions feel free to PM me
