I would have liked to see more discussion on Cannonfire Concerto, too. But then, I would like to see more nerdy character discussion on everything. 
I mean, Tally Ho is very popular, but apparently most players didn’t finish the game burning to write an essay on Haze’s psychological makeup, like I did. 
As for WIPs, I’ve said this before, but I feel that Your One Moment deserves more love than it got.
Same. I could handle never getting any updated again if at least I know the author is fine. They went on hiatus in such a worrying note!
I know, right? I know she’s very busy (if I’m not mistaken, she has a kid) but I do hope she keeps writing, even if it takes years for the game to actually be released.
I knew I was forgetting something!! I meant to send the author a message on Tumblr to tell them how much I loved the demo, and then ended up forgetting. It’s literally one of the best ones out there.
Lots of games I had never even heard of here. Will be checking them out later as soon as I have the time!
I feel like Heroes of Myth is underrated, in that I don’t ever really see it talked about with the other super-long COG. It’s not perfect but it has really compelling characters, and a ton of choice and variability.
A game that I absolutely love and doesn’t get (in my very biased opinion) nearly as much attention as it deserves is Diaspora. Such a great, intrinsic world with amazing characters and a demo longer than some published games 
Really recommend everyone giving it a try.
Psy high .choice of magics .heros of myth .wayheaven chronicles .werewolves, and pirates pleasure. Sword of the slayer Are my favorite ones
Wips I love and worth a million reads
Golden rose
Shepard of haven
Guenevere
Triaina academy
What a brilliant existence
Mind games (obsession)
Good intentions
Monsters
The passenger
Demon (recollect )
For publish cogs, Blood Money felt so much like a game made for me, and I would love for more people to check it out. You are a spirit medium whose sister is in charge of a crime family in a dark fantasy venice sort of setting, and its just…fantastic!
As for WiPs, one I feel deserves more attention and hasn’t been mentioned here yet is Roots. The game does such a great job of capturing the feeling of “just trying to get by,” which makes the MC getting wrapped up in mythological shenanigans all the more satisfying and easy to immerse yourself in.
I really enjoyed the entire cast of “Thieves’ Gambit: The Curse of the Black Cat” and wish it would of had a sequel.
“Choice of the Pirate” was also very fun and “Choice of the Deathless” was quite funny.
Foraker is a fun one, I also think Pon Para is underrated.
Right now everyone is hating Street Jam: The Rise and I think it deserves more love. Many people hate because of the things that are said in the warnings when you start the game. I think its really sad because I really like this game and I think more peaople should try it out.
Ooh, how much time do you have 
Honorable mentions for me are: Heart of the House, Welcome to Moreytown and Congresswolf. The former two are games I replay every now and again and Heart of the House isn’t my favorite, but a game I thought should’ve gotten a bit more hype than it did.
Trying to think of what games would be classed as underrated here so might be missing a few, and have a heap I need to finish reading 
Metahuman gets mentioned occasionally, but Orpheus ruse by the same author is also great and never seems to get any love. Last monster master is also a nice game that I never hear mentioned. I actually quite like Eerie estate agent too.
From HG I really like Tokyo Wizard and think it deserves more love. Scarlet sails is another one that’s a lot of fun. (For that matter the COG title choice of pirates is also good and used to get mentions, but pirates seem to have fallen out of popularity for some reason.) Highlands deep water is beautifully lovecraftian.
I’ll probably think of some more
Yeti’s Parole Officer is one of my personal favorites. It’s something short and silly, and the humor gets me to revisit it every once in a while.
One of my all-time favorite published games is one I don’t hear mentioned often: Deathless: The City’s Thirst. I think I’m just a sucker for tortured protagonists.
Couple others I really liked: Choice of the Petal Throne (a little linear perhaps, but a really interesting setting), Hollywood Visionary, and Fool!
If we’re doing WIPs – ugh, I have so many threads bookmarked, but a few that immediately come to mind:
Demon Bound
Nothing Left (To Burn)
Seven Days in Purgatory
Greenwarden
Bad Ritual
Mind Games: Obsession
(crashes through the wall in a shower of debris) DRAG STAR!
…
Okay, so I realize that Drag Star! was actually fairly popular for a while. BUT. I still feel like it didn’t get the recognition it deserved. Maybe this is just my bias because of how deeply I’m steeped into drag culture, but I feel like the game was overlooked despite being an incredibly fun homage to Drag Race and drag culture as a whole.
Another game that was actually pretty good was A Midsummer Night’s Choice. When I played the demo, I actually found it quite engrossing. Even though it’s Shakespearean, it’s not as dense, which was a welcome change when reading something Shakespearean.
EDIT: On the HG side, I adore Love at Elevation. It’s so quaint and the characters are surprisingly complex, which I didn’t expect when I first played through. The Ascot is another one that I liked for its simplicity.
Yes! I loved a Midsummer Night’s Choice!!
My Day off Work. It’s a unique creature, and presents one of the most entertaining true sandbox experiences in IF. Sure, there’s virtually no gamification to it, but that is part of its charm. Like a deranged older cousin of the original CYOA books. Maybe you strip and go to the beach, maybe you stay in and play WIPs, maybe you’re a hero, maybe you’re Sarah Connor. It’s a title where you know there’s zero chance you’ll run out of different things to do thanks to sheer volume.
Plenty of people have talked about Cannonfire Concerto, and I’ll agree with them. It’s a wonderful addition to the Choice of Games library, and it doesn’t seem to get that much love or attention.
Hollywood Visionary is also great! It’s quite unlike anything in the library, which I think is what draws me to it: there’s a unique way of using stats (your character has an inherent skill and a learned one, both of which are related to film-making), plenty of customization for making your picture and a stress mechanic, that increases the more work you take for yourself. The writing is solid and the characters are fun and engaging, to boot.
A Study in Steampunk is also often overlooked, for Hosted Games.
The lack of Dragon Racer in this thread is painful and enraging.
Keep in mind it is a thread about underrated games. Games like Dragon Racer that achieved a pretty good level of success could still be mentioned, but their omission would not be glaring.