I'm actually surprised to find that Luigi has a lot MORE strong points. He can in fact jump higher than Mario - and slow his descent like Yoshi can. AND he's taller and more athletic than Mario. And he's also Stronger too.
The only handicap that I see is that he's a bit of a Coward and a little too shy. Instead of barging into Danger Head-First like his brother, he's more than willing to hang back and let Mario take point.
When Mario uses a Final Smash he shoots out a massive fire ball and Luigi activates the negative zone which doesn't effect him, but anyone inside the zone. Luigi deeply cares for Mario and Mario doesn't really show love to Luigi. All I got.