Dev Emmet's courses typically were in the 6200 to 6400 yard range and only started to become longer when Alfred Tull was made a full parter. The best example being the lost course at Huntington Crescent Club.
As for a discussing his design style, he typically delt with very tight sites; thus, this explains he shorter courses. Contrary to what C&W and golfcourse.com write-up says, he often had raised greens with medium to large mounding around them. Other than his greensites and mounding behind fairway bunkers, he typically moved very little earth. He loved to have quirky holes and greens in odd locations. For example, if one plays the present Pelham course, when one gets to the present 7th and 8th holes, Emmet's original 6th hole played from a tee box up and left of the present 7th and the idea was to hit your drive just short of the present 7th green. Then have your caddy go to the top of the hill (tee box present 8th hole) and show you the line for your COMPLETLY blind shot up over the large hill to the original 6th green right of the present 8th. This is shown in Wexler's book with the interupted fairway being the large hill. Also, an FYI, the present first hole there is a Tull hole and not Emmet as the present DR sits on the old Emmet 1st. He liked to have one par 3 of gigantic proportions 220 to 240 and it often was a modified Biarritz type hole. He liked to have one short hole 110 to 135 yards, he like to have one VERY long par 5 550 to 585, he like to have several driveable or driveand pitch par 4 that played to well bunkered greens, and he liked to have several long par 4's. He was not afraid to incorportate blindness in to many of his designs.
He liked to build greens into the side of hills and have them fall off on two or more sides (1st at Webster Dudly GC, 1st at Immergrun GC, The Powelton Club #10). The Powelton Club's 10th hole may be one of my all time favortie Emmet holes. The hole is a mid length par 4 390 yards that plays slightly uphill to a semi-bling green off the tee. There use to be a long cross bunker that completly cut off the fairway that has been grassed over. The second shot plays to a green at the hightest point on the course that falls off by about 15 to 20 feet behind and 10 to fifteen feet on the left and the right. The green has two tiers and is triangular with the apex of the triagle in being at the back and the highest tier. On tournament days the back pin location on this raised small iece of green has dire consequences if you miss long!! I guess the members do not like the green and have been trying to change it, luckily, the present Superintendent knos a thing or two about golf architecture and will not let them touch it!!
As for reasons for losing so many courses (around 40 to 45) he lost at least 7 courses in NYC (Hillcrest, Laurelton North and South, Pomonok, Old CC, Queensboro, and Queens Valley), he lost 4 of the 5 courses at Slisbury Golf links, etc. I would say most of his courses were lost as a direct result of the depression, urban expansion or were built over (Fenimore, Briar Hall, Hartford, half of Congressional, etc.)
Sadly, several of Emmet's courses have recently been built over Bedford GCC, Briar Hall, Wheatly Hills (all bunkers redone Hurdazn & Fry and look nothing like Emmet, Ridgewood in CT redone by master restorer Rulewich, Mahopac, etc).
As for his most preserved designs Wee Burn is up there; however, Tom Fazio has been retained to redo all fairway bunkers!!
And, the present 2nd green is not Emmet and the original 8th and 9ths holes were changes sometime before the Women's Amateur held their in 1939; however, they appear to have been redone by Emmet. Mohawk GC in Schenectady is very good Emmet design that was not butchered too much by Kay, The Edison Club is very true to Emmet, Schuyler Meadows, Immergrun, Webster Dudley, Leatherstocking GC are all still very true to their original Emmet design.
However, Leatherstocking has altered at least four holes, the 3rd use to be a 245 yard par 3 that played over a large diagonal sand bunker that has been left to grow over, the 5th use to be a Road hole, and it appears the 17th and 18th were redone as the 18th use to be a par 3 playing to an island green.
Courses close to NYC that have a lot of Emmet left Brentwood CC has some amazing Emmet greens (upkeep is not that great), South Shore GC (Staten Island old Mayflower CC) has some very good Emmet greeens with a routing that is almost unchanged except for some tees being shorted due to higher volumes of play, Bethpage Green has a lot of Emmet, St. George's appears to be all Emmet except fot he 11th green, The Powelton Club has around 12 holes that are Emmet (route 9 and I-84 have hurt the club), Rockaway River in NJ is about 70 to 75% Emmet.
As for Glen Head CC, there have been a lot of changes to the course over the years and are almost too many to talk about. Even the layout in George Bahto's book leaves a lot of questions. However, if you compare the original Women's National scorecard (there is one copy in the clubhouse at GCGC) and Glenhead has a couple, a lot of the holes in routing and green location still appear to be Emmet.