Broken Bow 1-2
The Andorian Incident
Breaking the Ice
Shadows of P'Jem
Acquisition *Good episode despite it's blatant canonicty breaking
Shockwave, Part II
Storm Front 1-2
Cold Station 12
In a Mirror, Darkly 1-2
61 episodes out of 98 is what I deem what the most essential to viewing ENT. If you've never watched Enterprise follow this list and it might changed you opinion on this show.
I took the honest time to rewatch all of Enterprise last week after dropping out during the second season way back when. It left me plesantly surprised. While season 1 and 2 aren't much to speak of as is. I feel this abridged episode list will make it more than tolerable by cutting out the pointless BS. I'll always remain dumbfounded how Berman and Braga could have worked on so many episodes of VOY, DS9 and TNG and not have a working formula for this show. ENT should've been the crown jewel of Trek by it's debut with all the bugs worked out.
Season 3 kept me watching but the 9/11 and American wars in the Middle East theme's did grind my gears. The Xindi Conflict is comparable to the Dominion War although ENT used brevity in it's delivery of the conflict.
Season 4 without question has some of the best Trek episodes across the franchises. Manny Coto really redeemed the show and it's a shame they never a 5th season to continue with the direction many was steering it.
"These are the Voyages" only confirmed that Brannon and Berman had lost all sense of how to connect with the audience they were producing episodes.
P.S. I haven't completed Voyager so I won't have a list for you guy yet.