I’m too lazy to type it all, so I cut-n-pasted from Bulbapedia
[details=Spoiler]Features
Black and White returns features present in previous generations, such as day, time, abilities and the split between Physical and Special moves. Certain ones, however, such as Pokémon following their Trainers and the Battle Frontier, have been left out.
C-Gear
The C-Gear allows players to use certain multiplayer functions while anywhere in the game world. These functions vary with the type of communication used: wireless, Wi-Fi and infrared. The C-Gear is similar to the Pokétch in that it fills the bottom screen, but its applications are much different.
On the C-Gear, as well as in battle, the current time is displayed in 12-hour format, however, at the hours of 12:00 AM and PM, the hour displays as 0, rather than 12, as a 24-hour clock, such as that on the DS and in the Generation IV games, would display midnight.
Pokémon Global Link
The Pokémon Global Link is a multiplayer feature that makes use of the Nintendo Wi-Fi Connection and is the equivalent of the fourth generation GTS. In addition to providing the features of the GTS, it allows players to upload their save files to the Pokémon Global Link website to access the Pokémon Dream World. Players can also go to the Pokémon Center to enter Random Matchup where they can battle a random person also connected to Random Matchup. The Global Link is also the place where players can download exclusive content including C-Gear and Pokédex skins.
Pokémon Dream World
The Pokémon Dream World is a special feature of Black and White which is operated via an Internet website, Pokémon-GL.com. The Dream World allows players to send a Pokémon to the Internet to obtain items and meet other Pokémon, making the website in a way such that it is a Generation V analog to the Pokéwalker.
Many Pokémon that are found here are not found in the Unova region, and would otherwise have to be migrated from a Generation IV game to be used. All of the Pokémon available here are given Dream World-exclusive Hidden Abilities that their species cannot have by normal means.
Entralink
The Entralink is a new feature in Pokémon Black and White which allows contact with other players over local wireless. It is a multiplayer area in central Unova; Pokémon obtained in the Pokémon Dream World can be caught here. In combination with the C-Gear, it is possible to travel through Unova with other players and battle, trade and perform various multiplayer sidequests.
Pokémon Musical
Pokémon Contests, which have been present since Generation III, are replaced by the Pokémon Musicals. Similar to the Super Contests in Diamond, Pearl, and Platinum, Trainers have to dress up their Pokémon with different accessories. The Pokémon will then compete by dancing on the theater stage with the other entrants. They are held in Nimbasa City.
Seasons
Much like Generation II introduced a system of time, Generation V features a system of seasons. Seasons change every month, which cycles thrice for each year. With it comes aesthetic changes in the region, as well as some changes with the Pokémon found in the wild. Additionally, Deerling and its evolution Sawsbuck change forms every season. Some areas can only be accessed in certain seasons.
Sprite animations
While already featured in previous games, Pokémon sprites in Black and White remain animated throughout the battle. Additionally, full back sprites are now present in the games. Some, but not all, Pokémon use animated versions of their Generation IV sprites. All Trainers, on the other hand, with the exception of Bianca, Cheren and N, return to sprites with no animations.
Changing music
Whereas in previous games, the music was the same during entire battles (other than when the player’s Pokémon has less than ¼ health remaining), in Generation V, things such as battle music may change with the situation. For example, when battling a Gym Leader’s last Pokémon, the music changes to a remix of the main theme. The warning sound heard when a Pokémon has less than ¼ of its maximum HP remaining has also been remixed into its own music. “Rare” Pokémon also get their own theme. Although this isn’t technically new, the seasons change the music in certain places as well, though these changes are mostly the instruments heard. This is similar to the day/night cycle in Generation IV.
Triple battles
In a triple battle, three Pokémon on each side are sent out at once. There are restrictions as to which Pokémon can attack which opponent. The Pokémon in the middle can attack all three on the other side, but the ones on either side cannot attack the Pokémon on the far side of the opposite end. However, there are some exceptions to this rule, through the use of moves such as Acrobatics. The Pokémon Pansage, Pansear, and Panpour were introduced to showcase this new feature. The position of each Pokémon can be changed during the battle; however, a turn will be used up.
Rotation battles
Rotation battles are similar to triple battles in that three Pokémon in each team are sent onto each side; however, they are sent out onto a circular platform. The platform can be rotated a third of the way around without wasting a turn. The Pokémon which is in the third of the circle facing the opponent is the one currently active. Strategy revolves around predicting which Pokémon the opponent will switch to and switching to the appropriate Pokémon on the player’s side.
Gyms
Pokémon Black and White brings back the traditional eight Gyms, but with it a total of eleven Gym Leaders. They are Cilan, Chili and Cress (Grass, Fire and Water, respectively), Lenora (Normal), Burgh (Bug), Elesa (Electric), Clay (Ground), Skyla (Flying), Brycen (Ice), Drayden and Iris (Dragon). Cilan, Chili or Cress are battled if the player has chosen the Water-type, Grass-type or Fire-type starter Pokémon, respectively. Drayden is battled in Pokémon Black while Iris is battled in Pokémon White.
Elite Four
Unlike previous games, the Elite Four can be battled in any order. After battling all four, a path to the Champion is unlocked. The Elite Four members are Shauntal (Ghost), Grimsley (Dark), Caitlin (Psychic) and Marshal (Fighting). However, the player is not able to battle the Champion before defeating Team Plasma. Later, after defeating them in a rematch, the player will face Champion Alder, who uses a variety of types. It should be noted that Caitlin is the same person present in the Battle Castle who was alongside her butler Darach in Generation IV.
New Pokémon
Black and White bring a total of 156 new Pokémon, bringing the overall total to 649 from the 493 present in Generation IV. While some new Pokémon may have similarities to previously introduced Pokémon, none of the new Pokémon are related by evolution to any of the 493 introduced previously.
Battle Subway
Seven of the subway Lines involve battling. Like the Generation IV Battle Tower, the player may participate in Single battles, Double battles, Multi battles, or Wi-Fi battles. In each mode, the player must defeat seven Trainers in a row (two Trainers at a time in Multi battles) to earn Battle Points. Afterwards, the player can continue battling or return to Nimbasa City. The player’s total win streak is reported after each battle, and the player’s current win streaks and Battle Points can be viewed in the Vs. Recorder.[/details]
There are also changes to some abilities and moves.
Examples:
- Encore lasts exactly 3 turns (including the turn it was used) instead of 4-8 turns.
- Hi Jump Kick is now 130 BP, 10 PP instead of 100 BP, 20 PP like 4th gen.
- For Pokemon with the Sturdy ability, they can’t be KO’ed by moves when they’re at full health (pretty much an auto Focus Sash) in addition to blocking OHKO moves.