G&W's Bucket ***** Falco in the butt. Insurance against lasers is only icing on the cake. Bucket brake screws Falco and his low KO power over a lot. I should point out that one of Falco's biggest problems is that he isn't good at either edgeguarding or scoring KOs. (by the way, he's very good at gimping, but this is not the same as being good at edgeguarding)
The reason why B-air is good is because of what it does to shields, and because it is very difficult to dodge.
G&W can score KOs pretty easily with F-airs. Charge release on Smashes is also insane and extremely good on air dodges and spotdodges.
You can't hit him out of his Up-B, and his D-air can hit you out of your Up-B no matter what it is very reliably.
N-air, U-air, and Up-B make for some pretty broken juggling and edgecamping. If he reads an air dodge, and charges an Up-smash, it can kill you at ridiculously low percents.
Also, he has advantage vs DDD and ROB. Neither can kill him easily, and neither is particularly good at dealing damage to him either. He does better against Metaknight than the rest of the top tier cast except for Snake really.
Also lastly in teams, he's easily the best character in the game.
Really, G&W's main problem right now is that he's not popular with many top level players.