We've been several times and love it. We go to the mountains for the mountain/hiking experiences, though, so my opinions may differ from others posted.
I would skip Ober Gatlinburg... we thought it was pretty pricey for what it was, cheesy carnival rides... my oldest is 9 so I may have missed some of the stuff that was geared towards older kids, so someone correct me if there is more to do. There was a sledding type ride there that my kids liked (it was like you went in some sort of sled down the mountain on a track), but most of the other stuff bored my then 8 year old. The sky-tram ride up the mountain may be worth it though, it was a great view (I think you can just pay to take the ride and back.) And the food there was beyond horrible.
Cade's Cove is a wonderful drive.... if you stop often and get out and explore, it can take half a day. Roaring Forks, I think, is the name of the other driving trail and it's nice also.
There is a picnic area called Chimneys that is really nice, it has a stream running through it that is fun to play in/near if it's not cold (one year we went there for easter and it was freezing with snow in some areas! I'm from southern louisiana so that was quite an experience!)
Not too far into the park is the Laurel Falls hike... it's about a mile each way, I think, and it's a pretty decent waterfall to see. My kids love to play in it, again if it's not too cold. There are others but that's prob the easiest hike, and it's not completely "easy" (especially when you're carrying toddlers who suddenly cannot walk on their own

)
Dollywood is great, a must do, but make sure you check the schedule... not everything is open that time of year. They have a zip line there that looked fun but kind of pricey so we didn't do it. Likewise, alot of the Cherokee area is closed that time of year... I think all of it doesn't open until May (at least that was the schedule last year) but some of it is open... just check before you head out. But the drive through the park, where you'll go to get to Cherokee, is worth it alone. Amazing scenery. And right at the top is an area (you won't miss it, it's full of cars) where you'll get some of the most amazing photos... there are some rocks to climb and trails there also.
There is an indoor water park there also, Wild Bear Falls, it's not huge but it entertained my kids for about 4 hours.... alot of it is geared towards smaller kids but there were two big water slides I think. Dixie Stampede is fun if you like those kinds of things, but if you've been to any decent sized aquarium you can skip this one, otherwise you may enjoy it. Chatanooga has a great one if you'll be driving through there.
We always stay in cabins. The sugar maple cabins were all nice, but they tend to be in resorts where you have a cabin right on top of you. Last year we had a cabin from Jackson mountain homes, and there was a stream right off the back porch, no other cabin in sight. It was wonderful! Very relaxing. I love mountain vacations, much slower pace than Disney and you don't feel like you need a vacation after! Have fun!