That's awesome! I hope you have a wonderful time.
A lot has changed since you were last there, but a lot has remained the same too - that's just some of the beauty of the DL! Not sure where you've stayed at WDW before, but the GC is very much like Wilderness Lodge. The rooms are nice and the atmosphere incredible. The lobby is beautiful. And it sits right where the old parking lot was, next to DCA - so you're just a short walk away from DL's main gate. No buses to get around at DLR. Everything is walking distance.
At DL itself, some of the attractions that aren't at WDW include:
Matterhorn
Roger Rabbit's Car Toon Spin
Pinocchio's Daring Adventures
Alice in Wonderland
Davy Crockett Explorer Canoes
Indiana Jones - a must do!
Mr. Toad's Wild Ride
The Primeval World diorama on the train around the park
You'll find that POTC is about twice the length at DL vs MK
Space Mtn is "better" at DL
Fantasmic is shown on the Rivers of America - no seating like at DHS, but the show is much better at DL
Tom Sawyer Island now has Pirates Lair as part of it - and is pretty neat to experience
The Enchanted Tiki Room is the original show - no misguided Under New Management part of the show like at MK
DL itself has a much larger concentration of rides and attractions in a single park compared to WDW. You'll definitely notice the size difference since DL is much smaller acreage-wise, but the atmosphere and history is wonderful. I hope you have a WONDERFUL time.