No other Matt Groening series is like Futurama. Simpsons has it's ups and downs, The Critic only lasted two seasons, and the early days really don't count.
Then there's Futurama. A satirical sitcom WAAAAAAY before it's time that mysteriously appeared on the eve of Y2K, it has paved the way for sci-fi enthusiasts and modern animated sitcoms alike. Take the social commentary of The Simpsons, the nonstop jokes of MST3000, the wonky revitalization history of Family Guy, and the niche following of Community. You get the majesty that is Futurama.
Of all the seasons of the show, Season 4 is the perfect mash-up of all of them. It's literally the best by averages. You have some of the strongest standalone episodes like Crimes of the Hot, The Why of Fry, The Farnsworth Paradox, and of course Jurassic Bark. Jurassic Bark is enough reason to own season 4 of the show. It is the only episode of an animated series that WILL make you cry consistently. Even if you cannot cry because your tear ducts are blocked by a forest of bro hairs because your eyeballs are too manly, you will still have the feels. You have the commentary tracks of the creators David X. Cohen, Matt Groening, Billy West, and of course that charismatic Jon DeMaggio cracking you up every episode. You have the Play All feature that for some weird reason wasn't included in the first two seasons, even the Fox has rereleased them 3 times now. You have the subtitle tracks in 3 languages, and four different dub tracks, just in case you cannot speak English. And of course, you have all of the other great episodes of the series that are anything but filler, including the first open-ended series finale. A finale that will be the first of 3 series finales now. Audio is 2.0, but it sounds great even today. My only gripe is that if you cycle through the subtitle options during viewing, it somehow get's stuck on French for words that are spelled out on billboards and such. This was a problem with all four seasons of the original DVDs, but it's not enough to prevent a purchase.
As for the season itself, the laughs do not stop, the drama is at it's peek as Leela and Fry's relationship is pushed past the friendzone, the plot is ever thickening as the foreshadowed points from the past three seasons start merging together with Nibbler, and the supporting cast bring the show closer to it's magic Friends-type trope that it's now known widely for.
If you own any season of the show, Season 4 is as obligatory as Season 2. It's simply that good.