Jurassic Bark was one of the standout classics from the show's original run. Episodes featuring Fry's past are always an interesting set up, but this one knocked it out of the park with some great running gags and Bender sticking to the right side of offensive.
It's also most-certainly the episode with the most emotion, but if the original idea had been done, it could have been even more depressing. Before it was Fry's dog was fossilised, the episode was meant to focus on Fry's mother. That's right, instead of Seymour growing old missing Fry, it would be his mum (who was eventually written as distant and football obsessed).
Obviously, the writers realised that might push the depression a bit too far and decided to tone it back a little (not by much really though).