Which lego games are good? I'll look at the other games recommended here.
My kid only played Lego City Undercover, Ninjago, Star Wars and Pirates of the Carribean. On a surface level, they feel same-ish to me, in that they are all console ports with all the ailments thereof (clunky camera with the woes, you're pretty much expected to play them with a controller). Structure wise, you follow the main story with an additional free play mode in which you unlock various collectibles on the maps you've already beaten.
The games are impossible to lose, even though there are health "hearts", you immediately respawn nearby when you lose them all or fail a jump. So at the most, you'll get stuck on a puzzle,
but there isn't really a Game Over state.
Gameplay wise, it's usually a mix of combat (easy button mashing), exploration, puzzles, jumping (which can be infuriating because of the camera, good thing you get infinite retries) and some racing/obstacle runs.
The actual proportions depend on the game, e.g. Ninjago was pretty combat heavy while PotC went heavier on exploration.
As far as I could tell, port quality was shoddy in pretty much all of them, there were plenty of bugs like
random crashes, something not triggering in the code (solved by restarting the level), characters getting stuck, etc.
As to which one was the best, my kid played the Ninjago one to 99% completion, so this one was probably the best for him. From my perspective, the PotC probably had the best puzzles,
but it was possible to get stuck because something bugged out, or the game didn't communicate what you're expected to do.
Undercover looked really good, but your kid needs decent English to really appreciate it (the previous two were pretty language independent, and there's not one word spoken in PotC).
It felt a bit like a family friendly GTA. I might revisit it because we didn't have a controller at that time and driving was crap on the keyboard.
We didn't like the Star Wars much, I especially loathed the controls for space flight and space combat.