Umm, it's not good. The buses only come at specific times, not every so many minutes like Disney's. Then, you have to ride it around to several different hotels before heading to the parks. When you get to the parks, they drop you off in the middle of nowhere -- the same place where tour buses go, if you know where that is. So, it can be a decent walk to the park entrance and, if you have kids, that includes across a busy parking lot. Finally, at MK, they take you to TTA, so you still have to get across the lake before getting to the park entrance.
Bottom line -- if you're taking their buses, plan lots of time to get where you're going. And, don't plan to leave the parks whenever either, as those are on a schedule also.