Pokemon HeartGold and SoulSilver are the official remakes of Pokemon Gold and Silver. HeartGold and SoulSilver take you back to the regions of Kanto and Johto with some things you may remember from the old versions. New features have been added to the remakes of Gold and Silver. The game uses "IV Generation Aspects"! Play Gold and Silver in 3D with a new feel. Walk with your Pokemon, Legendaries of Hoenn/Sinnoh, and more features! Also, new events, Giovanni appears, Arceus uses its power!

New features:

• A key item "GB Player" lets you replace most of the bgm with Gameboy-style tunes. Even a few new songs have GB versions created. However, all Kanto music uses G/S instead of R/G/B music (with some exceptions where there was no G/S song, but in others of these new classic-like music was made like Cinnabar). I actually like most of the remixes, so I keep it off. The only remix I hate is Goldenrod's.
• Cerulean Cave not only returns but took me way longer to explore than in FR/LG. Its lv70 Mewtwo was my Master Ball pokemon in the game. Viridian Forest, Rock Tunnel, and Whirl Islands are like the same size as in FR/LG. Mt. Moon, however, remained small (and strangely doesn't use the remixed Mt. Moon song that some other caves do). You are not permitted to explore beyond the lobby of Silph Co. and the Kanto Radio Tower. Pokemon Tower remains torn down and Pokemon Mansion is buried under a pile of rock.
• Defog is, thankfully, removed. Its HM07 is now Whirlpool. Rock Climb is still in the game; although not useable until getting 16 badges, rock climbable walls are scattered throughout both Johto and Kanto. Whirlpools are now like 3x3 in size rather than one tile. The two most notable field-use non-HMs include Flash, whose TM can be bought at Goldenrod and which is heavily used in a majority of the caves, and Headbutt, which can be repeatedly taught by the tutor but is seldom useful. Although Sandshrew is HG-only and must be traded to SS, I used it any Psyduck as my HM slaves. Sand has Cut, Rock Smash, Rock Climb, and Headbutt while Psy has Whirlpool, Waterfall, Strength, and Flash. I gave Lugia Surf and Fly.
• Probably because of the 3D-ization, many things in both regions seem much more spaced out and less space restricted. Some other overworld notes to make include additional sound effects (like water flowing sounds stronger when close to a pond or bgm fading quieter in certain areas) and ladders' first 3d gen appearance going so far as making a climbing animation and being used heavily in pretty much every cave.
• The Magnet Train is completely useless to me. Both the gate between Victory Road/Rt22/Rt26/Rt28 and the entrance to Indigo Plateau can fly to and be flown to from all locations in the world.
• After finishing the Kanto gyms, the improved Elite Four is about on-par with Platinum's improved E4. They have slightly lower levels (by about 5), but each trainer is maxed at 6 Pokemon instead of the first four having only 5.
• There has been nonstop Wi-Fi events so far. As soon as one ends, another starts. These events include an Eon Ticket equivalent that lets you catch the nonroaming Lati@s in each version, two Pokewalker courses (including one with both flying and surfing pikachus), and a Mew. Unreleased and unannounced events even in Japan probably include Celebi and more pokewalker courses.
• Such features as Battle Frontier and Pal Park do return like other 4th gen games... but they're a complete copy+paste. Nothing changed besides the battle music as far as I've seen. Pal Park fills the gap that Kanto's Safari Zone left and Battle Frontier is where Crystal's Battle Tower was (Olivine). Though I would need Japanese GBA games to see this myself, I've heard that there is now no wait between migrating pokemon, but you still have to enter the catching game for each set of 6.
• PokeWalker is a somewhat nice little device. The points called "Watts" are earned for about every 20 steps. 10 of these let you attempt a wild battle with one of the course's available pokemon (with a battle system completely different from main games and more simple). The variety of available pokemon increases with how many steps you've walked it while in the course. The walker's wild does not generate much variety in each pokemon; only its IVs and nature, not gender nor moveset, dunno about shiny. Its itemfinder is useless.
• Pokemon following you in the overworld is something that should have been implemented long ago, including overworld sprites for all Pokemon. Following pokemon are strangely in constant walking animation; I believe this is probably to prevent flying pokemon to appear to float when still. They return to the pokeball with bicycle and most HMs (unless they're the user, then they jump in front of you to use it). If the first position is fainted, then the next healthy pokemon is let out, but pokemon cannot faint while walking anymore; poison status is removed at 1HP for any pokemon in your party. Unlike PC sprites, these sprites include shiny coloration, but some of the shades used seem quite a bit different than in the battle sprites.
• Like in Platinum, Foreign Dex exists for all Pokemon. However, at least in the Japanese version, all foreign entries are taken from Diamond (the same dex entries cookies uses for pokeguess, so I recognized them easily). English version may have only the Japanese entries be taken from HG/SS and others from Diamond.
• Unlike FR/LG, there are no trade nor evolution restrictions ever. Although a few 4th gen pokemon that evolve through learning a new move are included in the Johto dex, I don't believe I saw any Johto trainers using them.
• Most of the redesigned menus are nice. The only one that I dislike any aspect of is the PC box interface, which removed the ability to mass-select multiple Pokemon. Besides that, it is completely different in several ways from previous 3rd+4th gen boxes. Pokemon are moved mostly through drag-and-drop. In "Move" mode, which is still the best one to use, the party prompt may be opened either on the right (over the gap where summary/mark/release/etc appear when a boxed pokemon is selected, removing the ability to use that while it's open) or on the left (covering the box, but allowing use of that menu). Boxes cannot be switched while holding a pokemon, but you may drag a pokemon to the minipreviews of boxes where it is stored in the first empty slot. The top screen is dedicated to info on the currently selected Pokemon. The Pokedex's info on wild locations includes route names in addition to the map picture, but it does not predict Pokemon that may appear in the Safari Zone. Bulbapedia's location tables for each Pokemon are not quite updated for HG/SS so I'd suggest not using them unless they finish them soon. The bag could have been better and also barely uses the top screen at all, but it's at least better than the horrible bag system in D/P.
• The things that Mom buys for you from the "friendly shops" are pretty much entirely berries. They're delivered to you via the PokeMart Guy that previously only gave Wi-Fi event items. This is the most major way to obtain berries. He also is the one who gives you Togepi's egg, I think. The berry planter is kinda nice and the plants seem to yield way more berries than in D/P; about 5 for each plant I've grown so far with a few exceptions giving only 3. It only provides 4 pots and tree growth works about the same as before. Though, the idea of having a garden in your pocket may be even more of a stretch than a bicycle. Not that 4th gen seems to care at all about bag having realistic capacity.
• In addition to the 2 roaming dogs like in Crystal, one of the Lati@s is roaming in Kanto. Groudon in SS or Kyogre is HG are added in the new Johto route (which heavily uses 3D layers, rock climb, and waterfall). The legendary birds and Mewtwo return mostly in the same locations as in FR/LG. Lugia and Ho-oh work the same as before. The only legendaries unobtainable in HG/SS include the Regi trio, all 4th gen legendaries, and of course the event-exclusive ones.
• Pokegear's phone is somewhat less annoying than before. Conversations are not forced, rather, you hear a ringing noise and it's initiated if you open the Pokegear while it still rings. Ringing stops if you open a different menu, enter a battle, enter a different map, or talk to an NPC and also stops after like 20 seconds. There is no size constraint on the phonebook. All trainers are listed in order of when you added them, rather than sorted by something like trainer class, even for gym leaders. Unlike the Fly map, Pokegear's map displays roaming pokemon and allows you to write a custom comment about certain locations using the vocabulary system.
• There is a Run toggle on the bottom screen which can be simply tapped. The toggle remains even after turning the DS off. Because of this, holding B to run is pretty much unneeded. Some puzzles and caves do make it be useful to turn off the toggle. The "start menu" items are all listed on the touch screen and can be opened in one tap or navigated to by D-pad after pressing X. The options menu's ability to make Start=X is removed (St/Sel have no function ever), leaving "L=A" as the only non-normal control option. In addition to Y's key item which is also on the touch screen, a second key item can be assigned to constant display on the touch screen with no button trigger. The "Saving a ton of data, please wait forever" is removed so saving is usually faster. Even after I completely reorganized my entire box, saving was the same speed as usual.

Special thanks to:

[NG]