some decks people make out to be so powerful have incredibly simple weaknesses, these are some of them and their weakness

beatdown decks: easily stopped by gravity bind, also most are full of equip cards so when you use bad reaction to simotchi with morale boost that becomes deadly to beatdown users.
weenie beatdown: dark ruler ha des, twin headed wolf, ceasefire...ect.
control deck: can be crushed by cards like mystical space typhoon and other cards that disrupt your opponent from making a play.
chaos decks: soul release, gravedigger ghoul, kycoo the ghost destroyer, the list goes on...basically just remove from play the dark and light creatures
exodia: card destruction, as for necross see section on chaos decks (exclude light and dark and replace with exodia pieces)
burn deck: beaten by water deck combo, legendary ocean or umi with tornado wall.
dragon decks: two words, buster blader.

in short any deck has a weakness and there is no such thing as an unbeatable strategy. the metagame has infinite possibilities. the best advice i can give new and old players is instead of using old strategies that have been played over and over agian do something original. no one will expect your move and most likely will not be able to counter if it has not been tried before to their knowledge. the strongest player does not always win, cunning can win the duel more often.

eli the duelist
eli_the_swordsman@yahoo.com- this is my email, mail if you want and i will reply if it is convenient to me or if i like the mail. hatemail is immature and rude so i just delete it.