Pretty good top 100 list (I'll try to make some select commentaries here and possibly later)
http://www.flickchart.com/Charts.aspx?franchise=157&perpage=100
Kurosawa 40% of top 10 (Ikiru, Seven Samurai, Yojimbo and Rashomon - High and Low #12)
City Lights (#2) and Modern Times (#21) are my favorites by Chaplin, The Gold Rush (#30) close and The Great Dictator (#36) also a classic.
>>>Digression<<< Another distinction worth making is OOP (out of print) or not. When I decided to upgrade from DVD to Blu-ray where possible, a few titles were already OOP. Among my favorites were:
The Third Man (#7 here) by the somewhat forgotten but great director Carol Reed. Outstanding noir, captures the post-WW II atmosphere and mood and maybe the greatest entrance in film history by Orson Welles.
Also, The Man Who Fell To Earth by Nicolas Roeg, which has become one of my favorite science fiction genre films (actually PERIOD, with 2001 and Blade Runner), and who inexplicably failed to crack this list. The horror genre Don't Look Now (see below) about five years ago polled as the top British film of all time - The Third Man was #2. Walkabout also makes some Criterion best of and favorite lists. The first two are imo must sees.
Don't Look Now: best British film of all time?
Don't Look Now, the 1973 chiller starring Julie Christie and Donald Sutherland, has been named the best British film of all time by a panel of industry experts.
http://www.telegraph.co.uk/culture/film/film-news/8311268/Dont-Look-Now-best-British-film-of-all-time.html
In addition to the Killing, Kubrick's Dr. Strangelove (just added to the collection) at #4 and Paths of Glory at #13 score very high. The latter has a great commentary track by Gary Giddins, arguably the preeminent jazz critic in the world.
Bergman is an extremely important director in the history of world cinema (The Seventh Seal #19 and Wild Strawberries #22 were early staples on the art house theater circuit), Persona #15 tops the list here. Giddins also wrote an essay for The Seventh Seal (as well as La Dolce Vita #32 - generally these can all be read at the Criterion site under their respective film/title), and notes that despite saying about a movie you are "supposed to like it" generally being the kiss of death, it isn't warranted in this case, it has held up very well in a timeless sense, and can still hold a mirror up to contemporary times. The same could be said of Wild Strawberries and Persona (and many of his other films).
Scorcese was a champion of the great British shared credit production/direction/writing team of Powell and Pressburger (both produced, former directed and latter wrote), even employing Powell's widow as his editor at times. Red Shoes #16, Black Narcissus #70, The Life and Death of Colonel Blimp (#63) and Peeping Tom (#82 - while Psycho added to Hitchcock's fame, this prophetic horror genre film effectively destroyed Powell's directorial career) are all noteworthy, though I like the first two best. Some of the best technicolor images ever put on screen.
Hitchcock has some of his best work on Criterion (though not Vertigo, North by Northwest, Rear Window, Psycho, The Man Who Knew Too Much, The Birds, etc.), albeit my favorite titles are OOP I think. Notorious #18 used to top Sight and Sound's prestigious once a decade international critic poll among his body of work, though Vertigo had the distinction of being voted #1 OVERALL in the latest poll (2012?). Rebecca #40 and Spellbound (Dali painted the dream sequence) are also excellent, as are early pre-Hollywood, British productions The Lady Vanishes (#50) and The 39 Steps (#54), though the latter two examples in which he was still finding his style and way, not yet fully mature and at the latter height of his powers and peak of his form.
8 1/2 (#24) is the first title by Fellini, but should be a lot higher, imo - top 10? He was stuck on his next project and not sure what his film should be about or what direction to take. So he made a movie ABOUT THAT. Good intro by Terry Gilliam (I have his Brazil, which is great in the supplements department but may be OOP, as well as Time Bandits and Fear and Loathing in Las Vegas) praising it. Amarcord is another one of my favorites by Fellini, as noted above La Dolce Vita is #32, and Nights of Cabiria (#80) and La Strada (#88) also make the list, I've seen some of these titles score a lot higher in both Criterion and at large polls.
Le Samourai #25 by Melville is hands down the coolest noir ever, clearly an influence on Jarmusch's Ghost Dog (not in the Criterion Collection, though I have the quirky Down By Law and Mystery Train).
Tokyo Story #27 by Ozu was top 3-5 in the Sight and Sound poll (see below). He is revered by many directors (like Wim Wenders, I have his recently released early Road Trilogy, as well as The American Friend, Paris, Texas and Wings of Desire - another one of my favorite movies), and this is his consensus best work. Ebert also a big fan, I think. Since you asked about supplements and bonus features which Criterion is renowned for, this has a recommended bio doc on Ozu. For many, their knowledge of Japanese directors is exhausted after Kurosawa, but Ozu and Mizoguchi were both also masters and towering figures in world cinema. The latter's mysterious and haunting ghost story Ugetsu made #79, could have been a lot higher and also comes with a nice Mizoguchi bio doc. Sansho the Bailiff is relentlessly bleak (about a well to do family that finds itself on the wrong side of a clan dispute and is sold into slavery), didn't make this list but makes some critics best ever polls - I think Ebert very high on this, as well.
Renoir (related to the Impressionist painter) is an extremely important director, The Rules of the Game #28 and The Grand Illusion #31 score significantly higher on some polls - not just for Criterion, but among the best films ever made. The River is in the collection, beautiful Technicolor, I think the first Western film shot in India (maybe color?) and was an influence on the great Indian director Satijat Ray.
Badlands #29 is Malick's first title, and one of your new titles Days of Heaven comes in at #35. My favorite by him is actually The Thin Red Line (not to be confused with the murder mystery doc The Thin BLUE Line). The New World which just came out is the latest title I added.
This breakdown is already getting TL/DR, so maybe I'll revisit it later.
As to stumbling on titles, a book by the critic David N. Meyer (The 100 Best Films to Rent You've Never Heard Of: Hidden Treasures, Neglected Classics, and Hits From By-Gone Eras) pointed to a lot of Criterion titles I happened to like, and that led to me exploring more. I found him to be a very articulate and insightful critic and kindred spirit with uncannily similar taste. He also has a Criterion commentary track on the Monte Helman classic existential road flick Two-Lane Blacktop, in the first and only acting roles by James Taylor and late Beach Boys drummer Dennis Wilson, with the always interesting character actor Warren Oates.
Some titles he may have highlighted or that I discovered independently later:
Battle of Algiers is shot in an influential quasi-documentary style with many non-actor extras, about the Algerian War of Independence against France and features one of Morricone's best soundtracks, Antonio Gaudi is about the legendary Spanish architect, largely without dialogue and augmented by a spooky, minimalist, electronic, Japanese score, Kind Hearts and Coronets a British Ealing Studios masterpiece and the greatest black comedy ever, Alec Guinness puts Peter Sellers to shame by playing seven roles, who the urbane and charming but aggrieved serial killer Dennis Price needs to bump off to receive a remotely distant inheritance (highest possible recommendation), Night of the Hunter was a one off directorial effort by Charles Laughton (played Quasimodo in The Hunchback Of Notre Dame), with Robert Mitchum as one of the most iconic and terrifying villains in screen history - where he tattooed LOVE and HATE on his knuckles, Le Doulos by Melville (see Le Samourai above) is another one of the greatest noirs I've ever seen, Videodrome and Scanners (awesome score by long time collaborator Howard Shore) by Cronenberg are among my favorites, Eraserhead by David Lynch (cool supplement interviews),
Fallen Idol by Carol Reed (The Third Man),
Spirit of the Beehives is a neglected but haunting Spanish masterpiece (also looking forward to the far better known Trilogía de Guillermo del Toro coming out in October, with Cronos, The Devil's Backbone and Pan's Labyrinth), Three Films by Hiroshi Teshigahara is a surreal, avant garde set by the director of the Gaudi doc above, the gritty noir Youth of the Beast and the pair of bizarre, surreal takes on the Yakuza genre - Tokyo Drifter and Branded to Kill by Suzuki are recommended, Sam Fuller's Shock Corridor and Naked Kiss, and
House is impossible to categorize (Scooby Doo meets The Exorcist?) but is over the top comedy/horror and bat #### crazy.
* Sight and Sound Top 100 Critics Poll - 2012 (most recent)
http://www.bfi.org.uk/films-tv-people/sightandsoundpoll2012/critics
) that were extremely well made and could also be appreciated by adults - also on Hulu for those with that option. 
