Shiek- 2, is she the fastest falling char or the fastest? Either way it's easy combo heaven for luigi
Pikachu- 5, can be pretty annoying, but lacks the killing umph that you got unless they manage to land an on-contact thunder or surprise you with a headbash or something
Snake- 9, utilt, grenade, ftilt, grenade grenade grenade... and he weighs a ton and doesn't die easy. This one is TOUGH.
marth- 6, he's got a sword, you don't, so he's got range. But he just seems all washed up in brawl and easy to get your stuff in on.
Ike- 5, if you're sloppy this is hard, if you're patient and use your fireballs and don't fall into his attacks, it's pretty easy.
Wario- 5, wario has great aerials and aerial control, but it's hard to outshine luigi. Stick to the aerial basics, double shorthop aerials, or just about anything into the godly sex kick, and wario starts having trouble showing off his strengths
Wolf- 4, not even Luigi specific. Wolf is overrated, learn how to DI and dodge the similar nature of most of his attacks and just watch how predictable he really is, and he ends up not that annoying after all with only moderate KO power
TL- 7, one of Luigi's tougher match-ups. TL is just like Luigi in his aerials-almost completely lagless, can combo, great use... except Toon link gets his with a nice disjointed hitbox sword, you don't. But his projectiles aren't so bad.
Falco- 5. Not much to say here.
Peach- 3, she's outprioritized AND she's lightweight
Bonus evaluation
Meta Knight- 10, and obnoxiously so.