21333 The starry night. Beautiful set, super fun build.

I would say pirates of barracuda bay but it retired the end of last year. Amazing throwback to 6285, and the full ship/ shipwreck scenes is amazing. Easily my favorite recent-ish build, but I absolutely love old pirate ships and collect them.

Medieval Blacksmith (21325)

DC Super Hero Minifigs and sets is what did it for me.

Apollo Saturn V, my favorite set.

If you’re fans of Friends, Central Perk is a good one. It was my wife’s first lego set, she is now on the beetle and then the vw van

We also like architecture sets of places we been

If you like Harry Potter, look at the Hogwarts sets (Clock tower, great hall) - they're not too expensive, can be joined together and have cute ideas and nice generic parts out of which you could always build another castle. You can even build simultaneously. Lots of stickers, though - I recommend moistening the parts with water and dishwashing detergent before applying, so you can still slide the sticker around.

I also recommend to have a look at the modular buildings. Like the Assembly Square, which is an anniversary set for the modulars and imo by far the nicest one out there right now. It might scratch on the top line of your budget, but prices will rise like crazy once it's retired, and it's well worth it.

I really liked the remake of kylo ren's shuttle from star wars ($120). A modular building might be worth looking at too.

For a cheaper one, the toy store is very well designed. Also fun that it gets meta with little LEGO sets on the shelf of the toy store.

Buy a few $20-$50 sets that you guys think are interesting looking. Then buy a few $100-$150 sets. After building and finding things you guys like about building, decide on a couple of bigger or one big set. Most adults can build any LEGO set, you just need to figure out your own type of build that is still fun and not tedious and boring.

Wall•E 😁

For a good reason haha! Such an awesome set anyone could enjoy.

Ferrari F40

It's perfection

Barracuda Bay gets my vote. It’s super fun and is great for display or play. Mine is surrounded by Lego sea life with pirates out in small boats fishing the shark infested water. An octopus is nearby as are many sting rays. Multiple monkeys have joined the constantly growing pirate crew along with the lone pig.

Voltron

Barracuda Bay for sure!

My Horizon Tallneck! Great kit, great display piece. I'd love for them to make more Horizon sets though.

My Horizon Tallneck! Great kit, great display piece. I'd love for them to make more Horizon sets though.

The botanical ones are all super cool and great room decor.

The London bus I have, or the SMB question-mark block I don't have.

recently built this Guardians of the galaxy ship!

first set over 1k pieces as an adult. I was obsessed with lego as a kid and just recently started buying myself some sets as an adult. maybe one day ill get one of those INSANE starwars ones that cost like $900

The botanical sets are fun, as someone who doesn’t have the interest in gardening, but who also really loves Bonsai, I adore that build.

Saturn V or Treehouse. Both have character and display appeal as well as fun build experiences. End of treehouse is a little meh but still worth it overall

The Saturn V.

I'm tempted sometimes to take mine apart and then build it again because that experience was so incredibly satisfying!

Starry Night is such a fun build.

21333

Ideas tree house 21318 is amazing, and currently on sale for $175. Well worth it.

Bluebrixx has awesome sets! Pretty much like Lego but more affordable and the details are awesome. Best sets imo are the Gateroom and the ZedPM (It's with LED 😍).

BlueBrixx currently has the license and is putting out some cool stuff:

https://www.bluebrixx.com/de/items?q=stargate

If you are outside Europe, however, you'll pay a good bit for shipping.

Also check out the models from Master Replicas:

https://www.masterreplicas.com/en-us/collections/stargate-2

https://www.letbricks.com/product/moc-126952-lantean-aurora-class-sci-fi-battleship-model1835pcs/

Have a browse on Rebrickable. You can buy electronic instructions, but you will have to source the pieces yourself via LEGO's Pick a Brick, Bricklink, and the like. I fancy building some of these myself at some point.

Gathering the needed pieces can be a lot of work if you go this route. If you'd rather just buy a kit, look at BlueBrixx, as already suggested.

It’s definitely Rivendell, my daughter is very rarely impressed by Lego sets and she kept coming by while I built it and commented on how beautiful it was. An honorable mention though would be the new blacksmith, it’s my second favorite build, although I haven’t built my lion’s castle yet, but I think the blacksmith will stay in second place unless bag end is even half as nice as Rivendell.

Honest question, what is the appeal of the Saturn V set?

I’ve had it myself, after purchasing a bulk via a local online marketplace, but I just can’t see it. Yet it still keeps being mentioned, whenever OP’s question is asked.

Is it about the building experience, which to me had a lot of repetition, or rather the historical and cultural relevance?

Lion Knights’ Castle Set 10305.

This is the one. The motorcycle piece especially is piece of art not to mention the minifigure's torso piece

Saturn V is great, but a white set can't possibly be best of the decade, as it's already starting to yellow :(

Nice now get Rivendell!

I have a great friend also into Lego. I gave him a gift card because I didn’t know what he has or what he wanted. He got to get exactly what he wanted and was really happy with the gift card.

Land Rover Classic Defender 90 (10317) fits into that price range. Looks amazing on display.

I got my friend the Nissan skyline speed champion set and he loved it.

Comes down to what they like

The Starry Night? Purely decorative.

If he’s into aviation and planes then I’d wait until the 4th of September and get the Concorde set for $200.

If he’s into Star Wars, get a UCS set, or basically any set from that line since every set in it is expensive and overpriced (in my opinion).

If he’s into cars go for some of the recent Lego Icons car builds like the corvette, delorean, Ferrari etc.

If he’s into marvel go for the battle scenes recently released of the guardians ship.

Or you can go down the route of getting some gift cards for him and he can get what he truly wants.