Falco was a very good character already, but he had two kinds of problems. On one hand, his chain throw was simply too good in some matchups and on some stages. On the other hand, Falco was subject to much of the same abuse that bogged down Fox, and Falco had no viable options to force some characters off the ledge. Those problems were very difficult to exploit, but at the highest level of play, they really held Falco back.
Falco sees his chain throw gone, but his down throw is still a very good throw to set up for follow ups. Falco is also more than compensated for this by useful and fun new tools in his recovery and with his back throw as well as, more importantly, the removal of the abuses and ledge stalling that always held him back. This trade balances Falco, but it does not really make him worse.
Balanced Brawl Bonus: Special Walljump Cancel
Falco can cancel his aerial Falco Phantasm and Fire Falco with a wall jump.
Other Major Changes
Down throw is no longer a chain throw.
Back throw laser now hits opponent back toward Falco.
Full Technical Change List
Back throw throw box properties: Knockback Growth (80 -> 25), Base Knockback (80 -> 90)
Down throw throw box properties: Angle (50 -> 45), Knockback Growth (130 -> 10), Base Knockback (45 -> 85)
Falco Phantasm: cancelable with wall-jump on frames 3-16 of aerial ending lag
Fire Falco: cancelable with wall-jump on frame 5 of launching and during aerial ending lag