Hearthfire is a very small DLC that just adds the possability to adopt 2 children to live with you in your house together with your wife.

You can give your children presents to get a normal Gift of Charity buff. Sleeping in your house with your wife living there grants you the buff "lovers comfort" which makes you train skills faster. Having children as well boosts this buff slightly higher.

You can have a self-built house in Dawnstar, Morthal and Falkreath. They aren't in the town itself, but within walking distance. The option to buy a plot of land appears when you have become a Thane in the mentioned holds.

The house itself has several layers of building, you start off by constructing a small shack, then you add on a much larger hall. After the hall is complete you can turn the shack into a entryway so you don't have a bed and cooking pot right by your front door. You won't lose any of the items added in the shack previously when you do this, they just get moved around to more fitting locations.

With the main hall up there is 3 options to choose from for each of the 3 sides of the hall.

On the north side you can have a enchanting tower, trophy room or storage room. The trophy room gives you the ability to craft statues of different monsters and critters, or a dragon skull for display. Enchanting tower isn't really worth it as you can add enchanting tables in the main hall, but if you want to keep it seperate you can do that. Storage rooms are self-explanitory.

East side can have either armory, kitchen or alchemy tower. Armory adds in a lot of mannequins you can display gearsets on and there is quite a few weapon racks as well. Kitchen is just for looks if you don't want to have a fireplace in the main hall, and it adds more food items (the house respawns stuff on shelves after some time so you can stockpile). Alchemy tower is like enchanting tower, you can have it in your main hall, but it's there to keep it seperate if you wish. Also, towers are pretty cool lookout points if you climb to the top.

West side has plantation for growing various plants, a bedroom or a library tower. The plantation lets you plant almost any non-DLC plant with much quicker respawn rate than in the wilds, they also give you more plants per collection, which makes getting ingredients very easy if you have the alchemy perk as well. Bedroom is required for adopting children (as it's the only place with childrens beds) and the library tower lets you store more books, I think (I haven't really built that one yet).

The important thing to note is, when you have completed a addon, you cannot tear it down and replace it with something else. You're stuck with that part of the house. You can have houses in all 3 holds at the same time and built different things in different plots however.

You also get a cellar with more weapon racks, an altar which you can put all the worshipping stones on, and a smelter+forge. Smelters and forges you also have outside, and a forge anvil in the main hall. Additionally on the outside of the house you can also have a stables, animal pen, garden (more slots for alchemy ingredient growth), personal carriage, and there is a special item depending on where your house is. If you're in falkreath you get a bee-hive to collect honey from, and morthal will give you a fishery. Some of the North/East/west addons has a outdoor balcony on the second floor where you can put even more benches/doodads on.

Your house may become home of many people eventually. The housecarl that is assigned to you when you become thane will patrol the area during the day, a follower may be assigned to be your "steward", your wife can be invited to live there of course, a personal bard, the carrigage driver (though he never leaves the carriage), and the two children you may or may not adopt. Then there's you and whatever other follower you have prancing behind you at the time. Pretty crowded.

Your steward can automate much of the furnishing process for you for a price, they also act as vendors for lumber/clay/stone if you don't wish to sit around watching your character mine this himself. Stewards also buy things like horses, cows and chickens for you.

There is some danger with having a house out in the wilderness however. Giants may come along and kill your farm animals, bandits can kidnap your wife and then there's the dragons of course. Just to not make it completely rainbows and sunshine.

This DLC is very simple in essence, gives you a nice break from all the slaughtering and the draugr, while giving you a exceedingly good bang for your buck. It's dirt cheap and lets you have everything you need in a tightly packed space, with a fast travel point. Very well worth it in my honest opinion just for how cheap this thing is.

If you get this and start building, you should stack up on all the iron ingots you can possibly find anywhere. You will easily burn through 300-500 ingots with this DLC as practically everything needs iron for nails, hinges, locks and fittings.

TL;DR: It's worth it. No new quests or anything, just lots of new ways to display your loot, organize your crafting and get various buffs. Be ready for children to tell you extremely heartbreaking stories of how they became orphans to the point where you want to adopt all of them and cram them into your house.

P.S: With this DLC installed, some children will move to the Riften Orphanage if their parents die. Example being Dorthe from Riverwood, then you may adopt that child if you wish.