Ok, so I just played a shadow monk for the first time in almost two years. We stopped an Out of the Abyss campaign when the pandemic hit, and we had only played a up to 7th level, where I was Monk 6 / Druid 1 (.mostly because the higher level monk levels only get you very situational things).

Well, we restarted the campaign, setting ourselves to 8th. I reworked the character to be straight wood elf Shadow Monk 8 with Elven Accuracy and Devil's Sight (yeah, I know people don't think they can have it, whatever, pretend I said blindfighting). 

In the first battle, I shadow teleported 40 feet into the air to attack a Vrock, got double advantage on that attack, and took no damage falling 40 feet back down to the ground (if I'd thought of it, I would have tried to stun it, too). Omg, that was probably the most fun turn I've had in ages, and now I want to stay straight monk just for more ki to do more crazy stuff like that... Not to mention running up walls and across water and being immune to poison and disease and and and.  This character is soooo fun, and the Tasha's additions really help a lot. 

That’s awesome you are having fun and that’s all that matters. 

I've had great fun with my (open hand) monk I took all the way to 19 (then took a level of cleric)

They are great fun and I woould not say their higher level abilities are very situational.

• Poison is a very common damage type and condition immunity is great
• Being able to run up vertical surfaces has been useful numerous times, often attacking flying monsters by running up the wall and leaping onto them 
• Diamond Soul is huge, one of the best class features in the game
• Being able ot understand all oother creatures is extremely common but I admit by the time you get it someone should be able to cast tongues if it is important (though depending on the DM they could see someone casting a spell as an aggressive act) it is a pity that monks tend ot not have the charisma so use their language skills to persuade, deceive or intimidate effectively.
• If you get to 18 Empty body is another really powerful feature you can use in any combat, especially if you are able toget it off before initiative. Resistant to all damage except force pretty much doubles your effective hit points and if they don't have blindsight or something invisibility is huge.