The thing about the last episode is that you don't really realize it's the end until you think about it really deeply. I was expecting a lot of references from the first season to clear up all the confusion about the storyline, which is why I thought it would be a 2 -parter.
Like people are saying, I think everything was cramped together to fit in the key parts, they probably had to leave out so many scenes that they wanted to add. Other people may ask "what's the point? why would you want it to be longer?".
Since it is the last episode, I was expecting (like I said above) a lot of references from the first season, the "Radio Active" thing was very clever, but that was really the only thing. And also, I was expecting some more characters from previous episodes to be seen.
In most Sitcom finales, they leave a lot to our imagination, which is a good thing, however, I personally think they left 'too much' for our imagination. I for one would have liked to see a better example of Dewey and Jamie's Mischief, a tiny bit more of Malcolm's Speech, perhaps hearing a bit of discussion between Lois and Hal about their plans (of course that is before it was shattered by the new baby), and a lot more.
Apart from the fact that too much was left for us to imagine/predict, I think it was a brilliant ending, with so many major twists. Francis having a proper job he enjoys, Malcolm expected to become president, a 6th child, Reese moving in with Craig and even the simple fact that Dewey is now the oldest brother in the household, which never occurred to me until the last few episodes.
Since it is the last episode, it was probably extremely hard to set a path for each main character while also trying to end it with a "Malcolm in the Middle" style where it was funny. I think the balance was very good, where they used mainly Hal and Reese to keep it funny and kept Lois and Malcolm to reveal the final part of the main storyline.
I find it easier to criticise what I thought was bad than what was good which is why it may look like I didn't like it but I actually did, it was probably the best episode in season 7.