From my limited perspective as a novice in both SSBM and in the current incarnation of SSBB, I see Luigi as simply gaining a different play-style.
I certainly enjoyed the strength of his forward aerial in SSBM, to the point of abuse even, but that strength seems to have shifted from his arms to his legs in SSBB. Granted, his back aerial in SSBM (at least from what I can remember), was moderate and effective - but it's gotten a boost. I can't go and... well, '*****slap' anyone anymore, not even with Luigi's back aerial, but the decency is spread around in a manner that breeds better comboing. Considering that SSBB gameplay mechanics tend to push games to higher percentages than in SSBM (and that damage percentages have not inflated in proportion to the 'death-percent's), I consider the extra comboing ability a blessing rather than a curse to the beloved forward aerial of SSBM - the opponent is that much closer to the death percents that much faster. It provides a disproportionate lead that could have otherwise been lost to an overpowered forward aerial (granted, early walls of pain or pseudo-walls of pain from the slap's nice knockback would have been... nice).
As for wavedashing... I'll never get over its loss. It was, to put it lightly, awesome to stand on one end of Final Destination and appear in the next second in the middle of the stage with a down smash ready to pound opponents into the sky. To be quite honest, I don't think there's any direct counter to say that the lack of wavedashing in the entirety of the game somehow has a silver lining to it (other than 'Well, <insert random character who isn't in the top tier> could possibly outmatch us', but who cares about the other characters these days -.- ).
However, one then has to look at the newfound survivability of Luigi. Being a novice who had essentially decided that the Fox players who waveshined were telepathically hacking the Gamecube console mid-game (my fingers couldn't button mash for jack, let alone tap in intricate button patterns in the space of fractions of a second), I'm thoroughly enjoying the ridiculous heights to which I can rise up from once spiked just over the edge. The fact that, while my recovery is predictable and punishable by any and all who wish to punish it, I at least have a chance to recover from the very bottom right edge of Final Destination's map layout is awesome to me.
Again, I'd like to clarify that I was and still am a novice - if there's something higher in the metagame of the experts that I'm missing, well... I concede to the points of others.
(( I had more ideas to post about, but I promptly forgot them as I wrote this <_< It's quite unfortunate in my opinion... ))
