BW without team preview could be horrible, but by other hand, it's not a good answer... "hey, I'm a horrible metagame, let's do something that broke part of what Pokémon is for fixing it at some degree", so, I could love to see team preview out from the game, and balance somewhat more the metagame.
Wishlist:
- Every Pokémon should have the same quanty of IV's... In that way, you should play more with the distribution of those IV's, making things more inclined to preparation, and also; I always feeled injust that some Pokémon are just worse... because yes and because random, all Pokémon should have the same number of IV's with just different distribution. When Breeding, the IV's should be a sort of random "mix" between the two partners, for example if the mother had 30 of speed and the father 20, then the baby can have between 20-30 +/- 1-2.
- Taking in account the impact that can make the previous point, a limit of 150 EV's or something like that on each stat, making more important the classic bulky attacking of Gen 1/2 if you're playing on offensive on place of just put 252 EV's of attack/special attack and speed and sweep right away.
- Generation 4 inserted a lot of broken moves being distribuited to Pokémon who could just abuse of it right away, at difference of Generation 3 and previous, and sadly, because you can just interchange with Generation 5, you can pass them! So... A good solution to this problem (for example, Stealth Rock being a TM on generation 4 is one of worst things ever that Generation 5 was unnable to help) could be that you can pass Pokémon from previous generation, but only eggs, and those eggs just doesn't carry any TM/HM/Tutor move when it hatchs, it also could be combined with the previous points to doesn't make any problem of compatibility and stuff. In other words, a rebuild of the movesets of each Pokémon.
To the last point, the unique users who can learn it via level up are all Pokémon on buttom tiers like Golem, the unique exception is Ferrothorn, but I think if he makes the unique OP user of Stealth Rock, he should just be banned from OU, and problem fixed if the games doesn't balance very well at all.
- A debuff of weather induced abilities: That is, on place of make them forever, they should only be of limited turns like Sunny Day move and stuff, in that way you can just buy time to shout down the weather, and at the same time, give space and time for the weathers teams to work, too.
- Some minimal change to the type chart: Rock Type should resist Dragon. Ground Type should be weak to Flying (in that way, your Flying Type friends can finally switch with a reason to those Earthquakes). Bug-Type should resist Psychic Type or Dark Type, whatever of both. Steel-Type should not resist Psychic or Ghost, making them neutral. Ice Type should resist Water. Poison Type should be super effective against Dragon or Figthing. Optionally, Flying Type attacks could be inmune against Ghosts, too.
That is, with those suggestions (and with natural reasons behind it, apart from balance) almost any type should have a similar advantage on any tier. Also, less Water Type Pokémon should be able to learn Ice Beam, that just make Grass Type innefective against them, when they should be able to destroy them. Fire Type Pokémon should have better movesets, too. Fire Walls should learn a move like... a heal move of 1/2 HP that can give them an extra resistance or something like that, and Fire attackers should just have better coverage and optional moves... apart from Will-o-Wisp, derp.
I could rather buff a bit the Normal Type moves, too, because they can't do Super Effective with it's stab, then should have some of extra punch on their attacks, at least, like Double-Edge with 140 of BP and things of that sort, while Dragon Type moves should have a minimal debuff on it's BP, like they were before Generation 4, with Outrage having 90 or 100 of BP, and Draco Meteor with 110 or 120 of BP. A more balanced special Flying and Normal Type attack should be done and had better distribution, Porygon is ok with Tri Attack, but there're other sad Normal Type Pokémon with high special that can't use it at all, like Pidgeot or Noctowl.
Rain Dance, Hail, Sunny Day, and Sandstorm (and Trick Room) should be on the field for 6 turns without need of an item, and with the item, should be 10 turns (not item for Trick Room, please), I think, That could make more variety with the thing of weather inducers if the debuff to it's abilities is applied.