To me it most definitely leans more towards the sandboxy type game. You can imagine anything in your head and pretend it's happening. What it doesn't do is simulate RL, at least in my opinion. Life is not always rainbows and puppies, tragic and unexpected things (both good and bad) happen. In life, you decide what direction your life goes after those events. In TS4, nothing unexpected happens, unless you "force" it to happen. That's not a realistic simulation of how life is.
Does it have aspects of RL? Sure ...... you can get a job, get married, create a large legacy, split up, have babies, pets, and die. But except for aging and dying of old age, none of those things happen without the player directing it to happen. You don't see your neighbors living their life in this life simulation game ..... they're not outside mowing the lawn, raking leaves, shoveling snow, kids aren't setting up lemonade stands in front of their house, you don't kids riding their bikes, playing tag with each other or hopscotch on the sidewalk, you don't see your neighbors having a fight on the front lawn, nobody is getting arrested, you don't see people moving in and moving out, nobody is in their backyards BBQ'ing or having graduation parties or baby showers. There aren't even graveyards or funerals. None of these things happen unless you, the player, creates those scenarios.
But, TS4 is awesome for storytellers and builders tho, because they don't have to worry about the game intruding on the story line they have in their head and the team has given builders great tools to be creative with (within the limitations that they set, because we still are stuck in a world they decided which we can't edit or modify and we are still forced to live in only the apartments in the worlds they decided.)
Although I do love to build and redecorate, I also feel that the game lacks actual gameplay and unique activities that encourage you to explore the different locations and try out different activities, and possibly inspire you to create those new story lines you want to pursue. For example, why do we always get the exact same type of community lots? (Bar, Lounge, Library, Restaurant, Cafe, Nightclub). Why doesn't the team create new and different types of venues, like movie theaters, grocery stores, arcades, etc. that sims can go to? Yes, I know we can sort of make these things ourselves, but it would be nice to have them actually be an official functioning lot without having to make everything a bar or restaurant to encourage NPCs to show up and actually use the stuff.
Instead they fill the world with a lot of fluff, create these beautiful environments that are nothing but something pretty to look at. Like they were so proud of the fact that they made interactions for the new town square buildings, seriously? My sim can "window shop", as in peek into a window, not actually shop, just "pretend" they are interested in what is inside. The store, is nothing but a dresser, your sim can change their clothes if you click on, why would I have my sim change or try on clothes in the middle of town? Are these different clothes than what is available in the dresser or closet at home?
No, the game doesn't simulate much life for me.
And I do agree with the others about how this version leans heavily into buld/buy (mostly buy because we hardly ever get new walls, floors, foundations), which I'm perfectly ok with that because decorating is one of my favorite things to do. But, it's mostly because this iteration does not inspire or excite me to actually play in live mode.