Rivendell.

The most spectacular set ever released.

I'm excited to get my own copy of the Lion Knight's Castle soon! I think the modular Ninjago City sets are really cool and similar quality in terms of display and play features, however the first two sets of the series have risen dramatically in price. I'm sure the City Gardens that just retired will start to rise as well.

Rivendell or the Dungeons & Dragons set hit the same for me.

Rivendell, the d&d red dragon's tale, Barad-Dur, motorized lighthouse, treehouse, medieval blacksmith, A-frame cabin, hocus pocus house

Try checking out the Bricklink Designer Program! These are sets that are created by AFOLs (Adult Fan of Lego), and are official Lego sets. Each one has a "crowdfunding" round, and the sets will ship out about 6 months afterwards. Wave 4 (starts funding in February, ships in July) in particular has a few castle sets that could go with your Lion Knight's Castle (like the Medieval Seaside Market), and Wave 5 (which starts funding in June, ships in October) has a very innovative Mushroom Village! The few caveats I might note, though, are that some sets may sell out within a few hours (so be on quickly to get the sets you want), only digital instructions of the sets are produced, and some of the designs aren't as "polished" as a wide-release Lego set, meaning some structures could be weaker than you expect. Overall, though, I've been very happy with the sets from the program I've gotten.

https://www.bricklink.com/v3/designer-program/series-4/main.page

The pull back motor cars are great.

Otherwise, I'd go Star Wars or Marvel, something that has appeal beyond it being a toy to play with.

So speed champions are very good value. Another option since you don’t know his interests maybe go with several smaller sets with alt builds. Target has sale so for ~$30 maybe Lego mighty dinosaur 31058, Technic dump truck 42147, then a small Lego city or ninjago set.

When they did this at work I tried go for variety when I could but that leads to trying to decide what best “combo is” Now you said $30 but right now target has the large creative box on sale for $33.

You can’t go wrong with Speed Champions sets.

Speed champions. The countach is awesome if that is still available.

Speed Champions. Any of them.

I have alot of Dragons Rising sets and out of the current I have I would say:

Source Dragon Of motion, Thunderfang, Cole Titan Mech, Lloyd's jet mech.

I am close to collecting other sets soon like the one with the temple bounty or empress beatrix vs elemental dragon

Difficult to decide. But if recently LEGO can make a Monstrosity Kai minifigure (all grey except only headband red) I will definitely buy it.

It depends. Do you just want to build once and use it as a decoration or are you looking for experiment? Toycra has a good sale going on right now. Have a look!

Lions king castle and the D&D castle

More than must have, would suggest looking at themes that interest you.

The must haves will always be in demand and sometimes make no sense to buy if we aren’t interested in the theme, but if it’s the build experience you are looking for, that’s a different call.

My suggestion:
https://www.lego.com/en-gb/product/yellow-construction-wheel-loader-60450
https://www.lego.com/en-gb/product/red-farm-tractor-with-trailer-sheep-60461
https://www.lego.com/en-gb/product/fire-ladder-truck-60463

The problem with 10698 is it doesn't have too much playability. You just build those very simple models and that's it for a 4 years old. It is better when he has more experience with Lego and can see the more creative side of Lego and his own imagination.

Here's all the sets that lego designed for the 4-5 range. Hopefully he'll like one of these themes

https://www.lego.com/en-us/categories/age-4-plus-years

There’s a great Bricks and Wheels Lego classic set: https://www.lego.com/en-us/product/bricks-and-wheels-11014

If it’s like other Lego classic sets, it will include an instruction manual for the pictured ‘example’ vehicles.

I’d guess he’d also like Speed Champions. Lots of cool cars.

Have a look at the 3 in 1 sets! Instructions to make 3 models from the one set.

You could try buying a used bulk lot? In my experience they usually come with lots of wheels/ vehicle parts and generally you get far more for your money than buying new. Speed Champions are really good but may be a bit complicated for a 4 year old.

Lego city police has a couple individual cars for 10 dollars each. I would go with those if you want to start small.

I enhoy the ones you can display like Art i really enjoyed the Mona Lisa.

i like lego technic sets, it’s cool to see how it all comes together

12v trains, they were very interactable with remote switches, lights, train parking etc, ultimately making it the closest Lego has gone to a true model railway system. Very fun to play with :)

My kids are more about the minifigures and accessories. So they build the set, and will play with it for a while, then it gets turned into pieces for whatever they are making. Half the sets I buy them are because they have cool pieces in them.

Last year for Christmas stockings I just went through pick a brick and ordered interesting animals and parts. I think they got more play out of that than they did out of the sets they got. If your kid likes airplanes there are usually parts that are wing or rudder or helicopter blade shaped pieces that are big and relatively cheap, the ones I bought are constantly being used.

The Stuntz sets are a lot of fun, I'm a grown ass adult and I love putting on stunt competitions on my desk.

All of the trains!

I assume the space monorail from the 90s was fun

Wall•E 😁

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

Ferrari F40

It's perfection

Voltron

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.

Barracuda Bay for sure!