If you want to stack blocks and build something really fast then TS4 is your game.
But if you want to design your own towns such as with an empty template you decide what the terrain is, the landscaping and the hills or no hills and water or no water, beaches or no beaches etc. then TS2 is your game. If you want to build basements with windows and you can see with the land pushed up next to one side of the house (terraforming) where a basement isn't always fully dug out, like in real life, then it's TS2.
If you want Sims who really don't care grandpa died a few weeks later, they may not care and just walk over the dead body, then play TS4.
But if you want the kids who don't live with grandpa to be upset or think about grandpa sometimes days or weeks after he is gone, then play TS2.
If you have to write down (TS4) what happened between Joe and Jean last week in your game so you can remember what you were playing, then play TS4. But if you want to be able to see what is the deal between Joe and Jean then play TS2 because they have actual memories that affect them for most of their lives, unless you fix something or repair a broken relationship or improve a situation.
If you want to know why two Sims are fighting on a community lot and TS4 doesn't show then play TS2 why, you will soon discover Jackie called Janey, Janey told Jackie (speech bubbles) something that happened to Joe, Jean found out through telephone gossip and or gossip on a community lot, now Jean is mad that's why they are fighting... who knew? you didn't because you weren't there, and don't play them, but TS2 Sims were there, while you fished with your Sim, then play TS2 speech bubble and thought bubbles actually matter.
If you are more into the goal of a game, getting a promotion, filling skills, gaining rewards for yourself then play TS4. But if you want a game that is about the Sim, and it's journey along life's bumpy road, play TS2.
If you like a designated lot type then play TS4. But if you want Sims to visit multi type lots on one lot where you can eat, watch a movie, buy some clothes and not have to hide things on floors Sims can't reach then play TS2. It welcomes multi type lots.
If you want apartment buildings full of Sims and you can visit their homes inside then play TS2.
If you want stray sick pets in your neighborhood play TS4.
But if you want to be able to adopt that stray, play TS2. If you want to put your dog to work so it can earn it's keep then play TS2, they can have important jobs and feel gain rewards.
If snow doesn't matter to you and it's ok your Sim kid built a snow 'person' out on landscape that you wondered if they didn't scrape off their fingernails trying to get some snow for that thing, then play TS4. But if big snow drifts matter and Sims can barely walk through a blizzard then if immersion matters, play TS2.
If you are thinking wow, you really shouldn't play in that water in an electrical storm you silly Sim but they do it all day with no harm then play TS4.
But if you know something like that would surely conduct a ligtening strike, wouldn't it, then play TS2.
If you are mistified why Sally isn't mad at her partner for cheating right in front of her face but don't mind, then play TS4.
But if you want Sally to not become a doormat and just take that sort of treachury then play TS2, you will find out if Sally minds it or not.
If it's really hard for you to suspend your disbelief long enough to believe a big light takes kids then play TS2, a real Sim will come and get your failing kids to take them from your Sim.
If you don't care what happened to that Sim child then play TS4.
But if you do care, play TS2, other Sims can adopt that Sim child. They are the first on the waiting list when calling to adopt. So are your mistreated pets.
If it doesn't bother you that Sims have to do very little to grow food, then play TS4.
But if animations and immersion matter to you when you grow a garden in a game, then play TS2.
If it matters to you what certain benefits certain veggies and fruits can do for a Sim, play TS2.
If you like plantSims and Simbaby pods then you will appreaciate them more in TS2.
If a family tree matters to you then play TS2, someday you may want to remember the great, great, great, great, great grandma.
If family photos don't matter to you then play TS4. But if they do, and you want the entire family in the photo and anyone else standing around, then play TS2.
If you like Sims being obsessed with selfies then play TS4 but if you want your Sim to remember they took or asked someone to take their photo play TS2.
If you don't mind your Sim is just teleporting every where in a game then play TS4.
But if you care what type of car your Sim can drive play TS2. Why have so much wealth if you can't have that helicopter, or limo ride to work, or that sportscar to drive.
If it doesn't matter to you that Sims won't die from illness and maybe you are glad play TS4. They don't even have to actually take the medicine or even get off their rear end to order it.
But if you think you should have to use some gray matter to figure out how to cure Sims with flu and or deadly flu and colds then play TS2.
If you are into just building pretty Sims then play TS4. But if you want your world to reflect more of the not so good looking side of life then play TS2, those Sims aren't all pretty dolls.
If you don't care about animations and simulation then play TS4 there is a text message, popup for almost everything. But if you prefer to see it happen, then TS2 is the game for you. Very few text popups. More spent on actual simulating.
If you are delighted with Maxis clothes and hair and never hanker to create something yourself then play TS4. But if you want the freedom to use free tools supplied by Maxis back in the day, then play TS2, you will soon find out how easy it is to add an emblem on a t-shirt or maybe something more complex such as a full outfit. You might find out you were a wonderful custom content creator and wished you had done it years ago. Or at least just as good as some of the stuff you saw by other creators. Not everything you create may turn out so hot, but I can bet you, you will find out you can do it, too. Sometimes you won't need anything more than Windows paint for some projects. Believe it or not.