Some corrections to Solivagant's list above:
Neuschwanstein is on the German current T-list.
Santorini used to be on the Greek T-list.
Sindou used to be on the T-list of Burkina Faso.
Monte Verde is on the current Chilean T-list.
Ras Muhammed is on the current Egyptian T-list (marine reserves of Sinai).
Chicago School and Death Valley NP used to be on the American T-list.
Great Western Railway and Manchester industrial landscape used to be on the British T-list.
And then Amritsar and Pharaonic temples have already been corrected by kkanekahn.

I've thought of doing this many times, but every time I try, I always start having fond memories of even the most banal sites. Beemster Polder perhaps being the best example, I really rather enjoyed my trip there, it was a glorious summer day, I met some friendly locals and got a sense of why it was unique.
Heck, some of my most memorable visits have been to the Struve Geodetic Arc and the Pile Dwellings.

European Palaces are always my bête noire, so I would probably give a list of them for the least inspiring sites, even though I understand they are worthy of a place on the list.

Having said that I would be interested to see what places others aren't so keen on.

I'm not sure whether a list of "least worthwhile WHS" is really adding value. When we look at which are the top 50 sites missing, all of us, I trust, try to consider outstanding sites we have in mind.

If we start thinking about which sites are the least interesting, however, I fear that we will end up with very individual and subjective lists. For my part, I can only say that I'm a culture buff - so natural sites in general have less fascination for me than cultural ones. Actually I would even prefer to visit Beemster Polder than any of the Beech Forests in Germany, even though I live in Germany. Meltwaterfalls' comment is similar: as you despise palaces, you will rate Beemster Polder higher than some of those palace/castle sites.

So is it really worthwhile indulging in such an exercise?

Indeed, bad idea, as it would give too subjective and personal lists.

In fairness I thought it was interesting, more in terms of generating discussion than coming to a definitive list.

A sort of Buzz Feed style "You'll never believe these 50 Places are World Heritage Sites!", surely everyone loves a clickbait list :)

I think it's not a bad idea. After all even the top 50 missing list is somewhat subjective but interesting nonetheless.

2 more of our "Missing" list sites have been inscribed

- Ephesus
- Speicherstadt and Kontorhaus District with Chilehaus

4 "Missing" nominations will be up for inscription in 2016!

- Architecture of Le Corbusier
- The Ahwar of Southern Iraq: refuge of biodiversity and the relict landscape of the Mesopotamian Cities
- Nan Madol: Ceremonial Center of the Eastern Micronesia
- Key Works of Modern Architecture by Frank Lloyd Wright

4 "Missing" nominations have been included in our potential candidate list for 2017 (not guaranteed!). However, our Missing list is making progress!

- Funeral and Memorial Sites of the First World War (Western Front)
- The Sacred Complex of Babylon
- Bagan Archaeological Area and Monuments
- Archaeological Site of Gobeklitepe

So, 2017 is a disappointing year with respect to this list where No major missing sites are included.

In 2018, Three sites are lined up for inscription.

Tr'ondëk-Klondike (Canada) CL
Gobekli Tepe (Turkey) C
Funeral and Memorial Sites of World War I (Western Front) (Belgium, France)

So, out of 119 missing sites , 11 are already inscribed (5 +2+4 +0) in last four years. 3 are lined for next year.

Six more sites are lined up for world heritage sites in next one or two year

Plain of Jars (Laos) C
Bagan Archaeological Area and Monuments (Myanmar) C
Southwestern Coast Tidal Flats (Republic of Korea) N
Scrovegni Chapel (Italy) C
Frank Lloyd Wright Buildings (US) C
The Sacred Complex of Babylon (Iraq) C

It might be worth revisiting the Missing List after the 2019 WHC. Five years, additional voices on the forum, missing sites becoming tentative nominations, and more than a dozen inscriptions might lend to another rich discussion.

Tentative List Additions since 2014 (Top Missing)
2015 Dreams in Stone – the palaces of King Ludwig II of Bavaria: Neuschwanstein, Linderhof and Herrenchiemsee (Germany)
2015 Syrian Hajj Road & Egyptian Hajj Road (Saudi Arabia) *Pilgrimage route to Mecca (Kaaba not included)
2016 Padova Urbs Picta. Giotto, the Scrovegni Chapel and the 14th century painting cycles (Italy)
2017 Early Chicago Skyscrapers (USA)

Els, it would be better if we mention Which missing sites are inscribed in Rankings page. We had these earlier version .

http://www.worldheritagesite.org/ranking/missing+sites

kkanekahn

This is primarily a data issue. We don't have the links in the database, so it's really hard to show. If you want to see those, you would need to let us know. What I can match is shown below.

select m.site missing_site_name, s.site_name2 site_name, s.site_id, t.name tentative_site, t.site tent_id from missing m left join sites s on s.site_name2 like binary concat('%', m.site, '%') and s.status=1 left join tentative t on s.site_name is null and t.name like binary concat('%', m.site, '%') and m.inscribed=0 where s.site_id is not null or t.id is not null

missing_site_name site_name site_id tentative_site tent_id
Ebla (Tell Mardikh) NULL NULL Ebla (Tell Mardikh) 1293
Varanasi NULL NULL Ancient Buddhist Site, Sarnath, Varanasi, Uttar Pr... 1096
Bagan NULL NULL Bagan Archaeological Area and Monuments 819
Monte Verde NULL NULL Monte Verde Archaeological Site 1873
City of Herat NULL NULL City of Herat 1927
Alexandria, ancient remains and the new library NULL NULL Alexandria, ancient remains and the new library 1822
Amritsar NULL NULL Sri Harimandir Sahib, Amritsar, Punjab 1858
The Sacred Complex of Babylon NULL NULL The Sacred Complex of Babylon 1837
The Sublime Karsts of Papua New Guinea NULL NULL The Sublime Karsts of Papua New Guinea 5064
Lake Titicaca NULL NULL Lake Titicaca 5080
Coron Island Natural Biotic Area NULL NULL Coron Island Natural Biotic Area 5035
Svalbard NULL NULL Svalbard Archipelago 5161
Petrified Forest National Park NULL NULL Petrified Forest National Park 5253
Southwestern Coast Tidal Flats NULL NULL Southwestern Coast Tidal Flats 5482
La Brea Pitch Lake NULL NULL La Brea Pitch Lake 5645
Jericho NULL NULL Ancient Jericho: Tell es-Sultan 5704
Andaman Islands NULL NULL Cellular Jail, Andaman Islands 5888
Death Valley National Park NULL NULL Death Valley National Park 9467
Okavango Delta Okavango Delta 1432 NULL NULL
Silk Roads Silk Roads 1442 NULL NULL
Nan Madol Nan Madol 1503 NULL NULL
Ephesus Ephesus 1018 NULL NULL

Not sure if any other sites can be mapped.

there's a field missing.inscribed
if you display this, it will show per site which missing sites are already inscribed
that way we are back at the same level of information as before