They are fun, and a bonding activity like anything else. My wife and I build sets together.
Everything from the Harry Potter kids ones all the way up to the Expert architecture sets.
They are an artistic outlet as any other, and as an artistic outlet, suits a wide range of interests. LEGO group over the last decade has branched out into lines of products, with the adult builder in mind, my first post on the thread has a link to many of these expert sets for perusal.
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That's 18 gallons of LEGOs.
Edit: Here is our 2019 Christmas one:
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