The rocket ride was just moved and renamed to Astro Orbiters. It’s no longer on top of that big thing where the People Mover was - it’s now on the ground just at the entrance to Tomorrowland…you can’t miss it.
The Swiss Family Treehouse is still there, it’s just called Tarzan’s Treehouse now. They didn’t change much else besides the name.
Country Bear Jamboree is gone and the Pooh ride is there now, but the Country Bear Restaurant next door is still there.
Downtown Disney and the Grand Californian hotel isn’t really in between the two parks - it’s more to the side in formerly unused parking space - generally, where all the buses used to line up and acres of dead space that had no use. Looking at Disneyland’s main gate, it’s to the left all the way up to Disneyland Drive (formerly called West Street until Disney bought the street from the city of Anaheim). Right across the street is the Disneyland hotel and the Paradise Pier hotel, from where you can walk right into Downtown Disney. California Adventure is more where the main parking lot used to be - they only left a small corner by the intersection of Katella and Harbor - now the Timon parking lot. (Hint, if you can, park in Timon rather than in the parking structure - the parking structure is one of the largest in the world, which is a real bummer if you park on the far end of it! It’s a lot simpler to get to the main gate from Timon - to accomplish this, enter Disneyland from the HARBOR entrance, not the Disneyland Drive entrance where the signs will direct you to. Exit the 5 at Disney Way and ignore all the “theme park parking” signs - take Disney Way straight, which will cross Harbor, and take you right into the Harbor gate and the Timon parking lot).