I was an Olimar main in Brawl, and I have the game since Wednesday, so I'm gonna post my thoughts:
First of all, Pikmin attributes are the same, but Pikmin toss does less damage, heck the white toss only does 3 damage per hit after it sticks to the opponent! In general, really got nerfed by a bit because of his new upsmash and amount of Pikmin. Only having 3 Pikmin because of 3ds limitations is a pain, so I thought they would make the Pikmin have more hp or make the AI better, but no. For me it seems they have the some amount of hp as in Brawl, and the AI, like others pointed out is worse. The Pikmin must be in your line, otherwise you can't use them, which really is a pain with 3 Pikmin. This also makes the Pikmin toss less viable. But in general I think the toss is one of the tools you have to rely on in matches, because in close combat Olimar got the biggest nerfs.
Grabs got a really big nerf. The range is smaller, it's like Smash 4's pivot grab range is like Brawl's normal grab range. And don't even try to kill with grabs when your opponent is under 200%, it isn't even possible with blue Pikmin. You can only use grabs now to set up some combos, like d-throw to u-air, nothing special or to fancy.
Jab is a bit slower, and one of his best moves, the usmash, got the biggest nerf. Range seems to be the same or a little worse and it has some startup frames and a big cooldown after you used it. The usmash is punishable and slow, so you can't shield pressure with 2 usmashes in a row. At least the knockback is still the same, or maybe even a bit better. I wasnt able to use superarmour whistle, but people here said they saw it, so it seems it has just a few armor frames, which is really sad, because it will be so easy to keep him in the air now.
His recovery is like villagers, good range but predictable. You don't have to kill your Pikmin like others said, I had the experience that you can recover from most positions with 2 Pikmin, maybe with 1 when you are really far away. Maybe you still want to toss Pikmin, for covering options and to land save (flying over your opponent won't be possible with 2 or 3 Pikmin by your side). It is weird, because sometimes I recover but the winged Pikmin didn't carry me with all my Pikmin, sometimes 1 or 2 fell off. Olimar will have problems with recovering from meteors, because his recovery is better for horizontal movement, so maybe you have to kill 2 or 3 Pikmin in this case, if you still have time for that. For mixing up your recovery, Sakurai gave us the option to act out of the up-b with any of Olimars aerials, which will help A LOT. Keep in mind that you can't airdodge out of the up-b and that you will be in freefall state after acting out of it.
Olimars fair seems to be same as Brawl, his bair seems to have a bit more knockback and his dair is also the same as Brawl(?) I'm not sure on his dair, the meteor wasn't easy to get, time will tell if it's easier or harder to land, or if it's really the same. I'm no fan of the new upair, it is a single hit with less range than his Brawl upair. You can't be in front of or inside your opponent to use it, you have to be under him to hit. Kill power is the same as Brawl's. Upair, and dair do have way more landing lag, bair and fair are as Brawl.
Now the good things. His nair is a useful tool, it has nearly zero startup and landing lag like Brawl, and most combos with it still do work. Dash attack, and up-tilt will be used more than in Brawl because you have to rely more on moves that don't use Pikmin, maybe f-tilt can be used like Wario's in Brawl to cover opponent's ledge options? I think d-tilt is too laggy to be useful. His general movement is somewhat better, because of Smash4 physics Olimar feels a bit speedier, dash, fast fall and rolls are all a bit faster. We'll see if dashing away will still be the better option for Olimar or if rolls will establish in his meta.
I think his best tool will be the f-smash, which got buffed. It has even more range than in Brawl (purple fsmash has same same range than Brawl purple dsmash) and it can still kill. I think pivot fsmash is a really good and surprising move. Dsmash feels like Brawl's with a little more knockback I think?
Overall I think Olimar won't be as much of a threat as he was in Brawl, because of the 3 Pikmin limit, his upsmash nerf and worse whistle, people now also have general knowledge about Olimar and his playstyle, he isn't a surprise character as he was in Brawl for most, but upper mid tier to high tier should still be possible. BTW I think the small 3ds screen helps Olimar, even in Brawl people told me playing against him was kinda hard because they could not see what he did, because he was so small and many animations look the same for uneducated eyes. Maybe people will run into charged pivot usmash when playing on the 3ds
(Please keep in mind that these are just first impressions, so take this with a grain of salt)
edit: Forgot to mention that you can still cancel the pluck animation into any move that uses a Pikmin, so even if you don't have any Pikmin and your opponent thinks you are helpless and dashes to you, b into fsmash or dsmash is still a thing
