I'm a Luigi main and have used Luigi almost exclusively in Melee and Project M. I've been playing SSB4 for about 45 hours so far (according to the 3ds activity log) and, naturally, I've been playing as Luigi again for the most part. In Melee and Project M, Luigi's lack of traction resulted in most (if not all) serious players basing their playstyle around his excellent ability to more easily wavedash quickly and farther than other characters. Obviously, with wavedashing having been removed in SSB4, this brings a great change to how Luigi plays in terms of approaching, spacing, movement options, etc.
This is not a bad thing, however, if you still play Melee and/or Project M. I played Project M yesterday and found myself to be much smarter with approaching my opponent, which I really liked. Becoming so used to playing Luigi without wavedashing from playing only SSB4 (since I got it during the midnight launch NA release) made returning to the games where he COULD wavedash feel much easier with that extra boost (or lack of movement restriction.) Personally, I feel like playing SSB4 taught me how to approach/space myself/punish a lot better with Luigi because I wasn't focusing on trying to wavedash as much as possible, but instead on actually fighting my opponent. Being able to wavedash again caused me not to take it for granted and thus I ended up using it more effectively. Because of this, I definitely won't stop playing those games because I think wavedashing (and how Luigi plays in those games in general) is fun - which is why I chose to main Luigi in the first place.
Luigi is still a great character in SSB4, though, even if you're used to playing him in the previously mentioned games. I was really curious as to how the developers were going to make him a viable character with the wavedashing removed, but I think they did a great job and I have no real complaints. In my opinion they changed his moves well enough that, along with the lack of platforms, he doesn't even need wavedashing in SSB4. He still has the same moves - so, that carries over from the previous games - but with some updates.
Remember how you never wanted to do Luigi's dash attack and if it ever came out it was on accident? Well, now it's really good in this game. It's great for approaching and at the end of the attack it sends your opponent in the air and away from you, which is really great for comboing. Also, his tornado is a lot better in this game too, and it wasn't even bad to begin with. The tornado can cover a lot of distance while attacking and is great for getting back on the stage and when in the air and being attacked from below. You can even still perform the rising tornado (and it's easier to do) which makes Luigi's recovery AMAZING because most of the time I have no problems recovering back to the stage even without using it.
Speaking of returning to the stage, another awesome addition is that sometimes Luigi will get his head stuck in the side of the stage when he side Bs into it, so it's kind of like they gave him a cling/walljump to give him even better options to safely recover to the stage! It's a lot easier to punish and hit with sweet spots with the landing lag and slower animations and things like that too, but that's probably true with every character.
So, yeah, Luigi is different, but he's still a very solid character that I would highly recommend anyone to play in SSB4. Especially if you had any interest in him in the other games, but didn't want to wavedash too much or something. I for one am going to continue playing Luigi in Smash 4 along with Melee and Project M because they all have things about them that keep me coming back and I love playing them all! Not to mention SSB4 seems to be making me better at Melee and Project M as well, so that's a huge plus in my opinion. I just have to remember the differences between them, like the advanced techniques and available options, etc. Oh yeah, and when returning to the good old Gamecube controller, don't forget to use the c-stick for like an hour like I did.