This is a hilarious episode from start to finish. Fry microwaving popcorn causing them to be sent back to the Year 1947 was a great beginning and Fry actually inadvertantly killing his grandfather when if he had done nothing, Enos would have lived was just as good. Zoidberg being found as an alien was a terrific plot as was Farnsworth and Leela's with Leela using slang she learnt from Fry when the words wouldn't be invented for over 60 years. The end is so disturbingly brilliant with Mildred on the rebound heading straight for Fry. Fry's logic does make sense since it would be impossible for her to be his grandmother if he was still alive so he of course allows her to use him. I love Farnswoth's line when they decide to just take the sattelite:
Fry: But what about messing up history?
Professor: Oh, a lesson in not changing history from Mr. I'm-My-Own-Grandpa. Let's get the hell out of here. screw history!
This episode is a classic and explains how Fry came to be so stupid (he lacks the delta brain wave). A hilarious episode and one of my favourites.