NOTE: This review is of the Japanese version of the game. Some stuff may change in the American version, though if history is any indication, nothing aside from names will. I imported it a while time ago, but I wanted to truly appreciate every aspect of the game before reviewing it, since Pokemon is my favorite franchise nowadays and I wanted to do it justice. I needed to use Serebii sometimes to look at Pokemon types/moves, and I had to check out a Walkthrough twice due to not knowing what do to because I didn't understand the text. But other than that, I could progress just fine.
Pokemon Black and White are the new installments of the main Pokemon franchise, introducing the fifth generation of Pokemon. There's a whopping 649 Pokemon now, and a new region called Unova. You're a kid who fights Gym Leaders and becomes League Champion, blah blah, we know this. The question is the same as with every new Pokemon game - are the upgrades worthwhile enough to catch them all
again? And the short answer, is still the same - for diehard Pokemon fans, they are. For someone who's never been interested in Pokemon, no. For a Pokemon fan that's tired of the formula, also probably not. Regardless, I will discuss them at length for those interested.
The first change any player's going to notice is the graphics. The engine is very similar to that found in the fourth generation, however there's a lot more 3D going on. While the game retains the overhead view, the characters are taller and thinner, giving them a more realistic look. There are speech bubbles now instead of plain text at the bottom of the screen, making conversations more dynamic. What's also more dynamic is the battle screen - the sprites animate, the camera moves to focus at the Pokemon that's attacking, and quickly shifts to the Pokemon that's being attacked, and just rotates around when the battle's idle. I thought this would slow the battles down, but believe it or not, they're actually faster than they were before. The Pokemon you're using is a bit pixelated since it's zoomed in so much, but other than that, I think this is a very welcome change to the games. The textures are definitely upped from Diamond and Pearl.

The second major change are Triple Battles. They're 3 on 3 battles. There are two types of triple battles - regular and rotation battles. Regular Tripple Battles act just like double battles, but there's a catch. See, there's 3 Pokemon on each side - one in the left, one in the center and one in the right. Your left Pokemon can't attack your opponent's right Pokemon. The only guy that can attack everyone is the one in the middle. Rotation Battles allow you to, well, rotate your Pokemon. This rotation wastes a turn, meaning, you can't attack the same turn you rotate. Let's say you have a Water Pokemon on the left and your foe has a Fire Pokemon on the right, you can rotate your guy to the right or center for super effective damage. Of course your opponent can rotate too. I think they're a welcome change and definitely add a bit of strategy, and thankfully they're not very common and often optional - very nice.
I should also mention, Black and White are probably the version with the most differences between them in Pokemon history (though they're still not huge, lol). Aside from exclusive Pokemon, each game has an exclusive area (they're in the same spot in the map, and you get to them after beating the Elite Four), White Forest and Black City. Black City is great for battling strong trainers and buying rare battle items in shops, whereas White Forest has
tons of rare Wild Pokemon unobtainable in Black, and you can also buy berries. At first they start out pretty empty, but more stuff is added as you use the local wireless aspect of the games. I'm not entirely sure how this works due to language restrictions/not many wireless friends, sorry. Aside from this, there are some cities/routes which have small aesthetic changes depending on your version. White looks more natural, and Black looks more technological overall. This is especially noticeable in the city with the Eight Gym. Speaking of, the last Gym Leader is and old guy in Black, and a girl in White. Their teams are exactly the same. I guess Black is the version to get if you're a competitive battler, and if you're a collector, White is for you.

The last major change is the Season Cycle. Aside from the day-night cycle that's been around since Gold and Silver (except in Ruby and Sapphire, but those games suck so it's okay), there are seasons now. They're not exactly like real life, though. Each season lasts one month, allowing for three cycles a year. It's Spring in January, Summer in February, Autumn in March, Winter in April, Spring in May, so on. These bring about obvious cosmetic changes, for instance routes will have snow in Winter, brown leaves in Autumn and the grass will look extremely green in Spring. And they also sprout gameplay changes you'd expect from the Pokemon franchise; some Pokemon are found in the wild only in Winter, for example. Or some will only be in an early route in the Summer, and won't be obtainable until much later in the other seasons. Or they might be common in Autumn and rare in Spring, so on and so forth. The music also changes in some routes depending on the season. The most major change is one specific new Pokemon which I won't spoil, which has four different forms - one for each season.
Speaking of, I gotta say I really, really like the new Pokemon. I will only show a few early ones in a picture below for spoiler reasons, but the majority of them both look great and have great types and movesets. You might be interested to know the Unova Dex is
only made up of new Pokemon, meaning, you won't see your old favorites after getting the National Dex (after beating the Elite Four, as usual)

There are also more minor changes that are definitely welcome. You have two Rivals this time instead of one (the classic rival, and a girl that picks the Pokemon that's weak against yours), TMs are now infinite use, Poisoned Pokemon don't lose health outside of battle, you can catch two Legendary Pokemon as soon as you get Surf, there is one huge, fully 3D city with many streets and stuff (you've probably seen it, they marketed the hell out of it), but it's nothing insane gameplay-wise, the first Gym leader has three types and uses the one that's strong against your starter, you'll occasionally find shaky patches of grass randomly (like those with the PokeRadar, if you remember) which contain rare Pokemon, and a few more.
There also are small, but very welcome new Wi-Fi features. Everything that was in the fourth generation Wi Fi is here, but now you also have Random Matches (finally), and live trades on the GTS, meaning you're paired up with a random person, you select a Pokemon of theirs and they select one of yours, (you can check out the other guy's Pokemon's stats and everything) and if you both approve of the trade, it happens. You can do this multiple times with the same person.
Everything else is the same. Of course it's different, but it's the same formula. You'll find eight Gyms with puzzles, routes, water routes, routes with weather effects, HMs to get, trainers to fight, wild Pokemon to catch, small side-quests to do, dungeons, an evil team, etc, etc. The touch menus/boxes from HG/SS return, but the "run automatically" button is gone, same as the Pokemon following you and the Pokewalker support. By the way, the music is GREAT. I was honestly surprised. A huge improvement over Diamond and Pearl.
Overall, if you expected a new Pokemon game with welcome improvements to the same old formula, you won't be disappointed. I think it's better than D/P/Pt, definitely better than R/S/E, and slightly worse than HG/SS, but maybe that's just because I personally love the Johto games a lot.
This new generation of Pokemon delivers on what it has always delivered and nothing more. Again.