This is complete awesome. There's all sorts of things to love about the break neck pace of events in this two parter. The humour and the drama come together really well. Rita/Zedd and Mondo going at it in the Rangers Zords, the first team up of two different Sentai teams, and one heck of a fight sequence on the ground. The sub-plot of Billy aging was probably forced by his departure from the show, which was clearly decided some episodes before this as he kind of vanished from the scene after Jason came back. Still, the actor they brought in to play old billy did a great job, and the plot itself is strong.
It is worth noting that american political issues come into play here a little as the idea of billy being in mortal danger is avoided almost to a fault. When deciding if he should return to aquitar, the alien ranger says 'I couldn't forgive myself if something happened to you'. Well, he'll be dead in an hour, so the point is moot. Still, as slightly awkward a moment as it is, it really doesn't detract at all. Curiously, despite this, the writers took a far more daring step with the shows other political danger zone in this episode. When Bulk and Skull are taking their detective exams, Angel Grove is under attack. This is the first time that the impact of that is made so clear. The roof is caving in all around them, with lights flashing out the window and a bomb siren. The bomb siren especially is a kind of haunting touch. It's a cool scene. That question still nags me though, how is Angel Grove not completely destroyed after these 4 seasons, and why is any one still living there? Why is school still in session. None of that really matters. It's the Power Rangers. I wonder though.