Is it worth the $5 i paid for it? Yes. Does it let you arrange the house as you like? No, not exactly.
Basically, it's to let you build your own house. There is some enjoyment to that I find, despite the DLC's limitations. It will take a lot of iron ingots--you can use the anvil outside (or the one you build inside) to create the nails, locks, hinges and fittings you need and you can improve your smithing that way. There are few new building materials like goats horn (for lighting fixtures), straw and glass that you can buy at general goods merchants (only goat horns can you get in the wild). There are also quarried stone and clay, and there'll be deposits of these on your land to mine, or you can get a steward and pay them to get them. And you need saw logs, which you buy most sawmills--the ones outside of towns/hamlets, like Mixwater or Half-moon. Or you can get your steward to buy some.
You get a layout (blueprint), you acquire the building materials, you build your house. You build a small starter house, then from there you build a main hall, various exterior additions like a smelter, a garden, an animal pen (for a cow and chickens) and a stable. And then you can add one to three wings, and for each wing you get three options.
Here's what pisses me off:
For the Falkreath house, you have a west, north and east wing.
West wing can be extra bedroom (in additional to the double and two single bed in the upstairs main hall), an enchanting tower or a greenhouse.
North wing can be a storage room, a trophy room or an alchemy tower.
East wing can be a kitchen, a library, or an armory.
For each wing, they can be only one of the three listed for them. You don't get to put an armory on the north wing or a kitchen on the west wing, for example. And if you want, say, a library AND an armory in that house, well, you can't.
When you've built the house, it sets up workbenches inside each part of the house and in each wing for you to create the interior stuff: furniture, barrels, chests, alchemy lab arcane enchanter, bed, etc. and stuff specific to the wings. You can choose to build what's available or not, but you don't get to decide where things go or add things--that's already preprogammed on a grid. It kind of sucks but it's not unlike with how the hold houses are set up. At least you can forgo creating the horker head wall decorations.
What I do like is that, hey, it's another house, and I do like building it. For my Wood Elf character, who's a smith, for example, having him build this home for his new spouse was prefect and I really enjoyed it. He'd work on it during the day, and go back to Breezehome in the evenings to be with his hubby and get a homecooked meal to take with him for the next day of building.
It's a much more roomy house with lots and lots of storage (so the storage room is kind pointless unless you want a nice balcony). You can have access to your own alchemy lab and enchanter, and if you're into the alchemy, the greenhouse to nice as it lets you grow about 18 different ingredients and when you harvest them you get 3 or 4 at a time, not just one. (personally I think the greenhouse is the best wing).
And there's a "safe" container outside--when you get your land, there'll be a drafting table, a workbench, an anvil and a chest. That chest is a "safe" container, meaning you can store things in it and they won't disappear when the environment respawns. What's nice about this is you can walk or fast-travel there, unload a bunch of stuff into that chest and get back to whatever you were doing without having to deal with load screen from entering a building. Seems like a small perk but I find it very handy.
If you complete the thaneship for that hold you get a housecarl. You can also hire a steward (most, not all, followers and housecarls can be a steward), who can then hire you a bard if you like. Add in two kids and a spouse, you have a pretty cozy little family there.
These things make it worth the $5, IMO.
Downsides I don't like:
Display cases are drop-and-drag, and frankly I've never been able to drop and drag anything in one without a huge ordeal to it. Then, half of the time, things don't fit.
The only bookshelves you get are in the library wing. So if you want to store and display books, you have to opt to not get the other rooms that wing can be.
Some redundancy in what you can build inside. It would have nice that instead of 12 safes scattered throughout the house, having more variety and choices.
If you don't complete the thaneship for that hold, you don't get a housecarl. And the housecarl helps ward off the annoying random attacks by paroling your estate (well, they're suppose to).
You can only adopt two kids no matter if you build more bedrooms or you build more than one house (and while I can't confirm this, I hear the kids really don't like the Marthol hold house and will complain about it being scary).