(NOTE: This review contains spoilers)
When the Turtles are caught sneaking a peek at Cody's journal, they're explicitly forbidden from doing so because knowledge of their future might have damaging effects on the timeline. So what do the Turtles do? Why, sneak a peek of course!
There's a certain sense of mild frustration upon finishing the episode, because it's all fake. It's all concocted by Splinter to teach his sons a lesson, so none of the stories really matter. This episode is basically fan service to anyone missing the familiar characters and situations from the first five seasons. But if you watch this episode again knowing the outcome, it's a fun ride.
We get to see April, Casey, Karai, the Justice Force and a few surprises, mostly because 4Kids skipped over the Ninja Tribunal season and aired this first. The stories are fluffy but fun - there's actually a pretty decent build-up with the stories starting pretty believable and moving to utterly ridiculous (as Splinter well admits).
Bottom line, if you're looking for anything substantial you won't find it here, but otherwise it's a fun look back on the early years.