Zauron has said just about it all - Olimar is a pimp, and is definitely above average in the tier. Rest assured, though, he's not exactly user-friendly, so I doubt we'll see too many people overwhelmingly preferring him in tournaments over more traditionally good characters.
I'll do my best to address the other questions I've seen come up in response to Zauron and HeroXL's posts, as I was able to get 3 hours of surprise Brawl in today (I had no idea I'd be playing it this early!).
Matt: I checked out all his taunts, and nothing in particular caught my eye. As a result, I invented my own taunt. If you turn around when you have Pikmin following you, they go through you in single file and line up on the other side. If you are completely against the edge, and then turn around, the Pikmin run to the edge and then jump STRAIGHT up instead of jumping off. If you keep pivoting back and forth like this, the result is a mesmerizing, undulating Pikmin wall on the edge of the stage (the Pikmin jump to about the height of a short hop).
I didn't pay much attention to his victory music or poses, so whatever. But I was curious as to the mechanics of his grabs, and was very pleased / intrigued with what I found out.
With normal attacks, the Pikmin that Olimar is using goes to the end of the queue afterwards, and the second Pikmin becomes the next. After Olimar's throws, this is not the case. I wasn't able to discern any sort of underlying pattern beneath the reordering, but this was probably due to everyone being too excited about playing the game and not letting me write down my Pikmin orders... Anyways, the opponent takes damage and is sent in a direction corresponding to the type of Pikmin used. This is an exciting property, because it would make it nearly impossible to DI correctly against a very skilled Olimar player! This could also lead to creatively complex chaingrabbing cycles (lol at alliteration) by professional players - using a function of certain throws and certain Pikmin to calculate their resultant trajectory and follow up with a chaingrab or a combo. GOD I sound like a nerd but I'm so stoked.
Amazingly enough, though, the best part of Olimar's throws is initiating them! Olimar has the best grab mechanic that I have seen thus far in any smash game! He has a ranged grab - sending Pikmin out to grab them - which is as fast as a melee grab! If you "miss" your grab, you aren't helpless like Link or Samus (or even Yoshi), you can attack, run, or even grab again! When I played earlier today, I was machinegunning his Pikmin out for grabs as fast as any character can grab at the air! This definitely was one of his best points in my book. It gives him a good shield grab game as well as a nice ranged grab for mindgames (combined with his ranged forward smash and his Pikmin toss for Mental ****!).
His up throw involved a Pikmin grabbing the enemy, jumping a short distance, then slamming it down. The enemy is sent up and out. His down throw sends them a short ways up and out. His forward and back throw send the opponent where you'd expect. The back throw was his farthest, while his down would be the most suitable for chaingrabbing or comboing. Sorry, I don't remember what many of them look like. They were'nt very visually impressive, but that's okay. Olimar doesn't need to compromise for ANYTHING!
IllidR: I was really happy with his tilts. Their most notable property, besides being Pikmin-less, is that they all involve significant movement on Olimar's behalf for the attack. His up tilt, as previously described, has him jumping a short distance off the ground (a few feet) and spinning, with good priority and damage. His down tilt has him sliding across the ground in short, headbutt bursts. His side tilt is the fastest of the three, and has him lunge out a short distance (Ness' bat's range) with his feet, before falling on the ground. The move is quick, moderately strong, and has surprising range. The drawback is that you are vulnerable on the ground for a short time afterwards. I'd say it's worth the tradeoff, but it's a move that should be used sparingly. The up tilt sends enemies up - the forward tilt sends them forward, and the down tilt sends them back and up (if memory serves, maybe I just made that up though). I think these three attacks are excellent additions to his arsenal even when he has Pikmin, as they represent more erratic speed and position changes to further confuse your opponent.
His d-air had good priority and, because it involved Pikmin, a disjointed hitbox and decent range. I had no problems connecting with it. Still unsure as to it's Spike or Meteor Smash nature, though.
I know exactly why you're wary about Olimar being related to Marth. I hate playing by the tier, and switched from Peach to Pikachu for that reason in Melee. At the very least, it shows how much potential he has. But believe me, Olimar's potential is much different than the generally noob-friendly Marth. Mindgames are going to be a huge facet of Olimar's play, and advanced situational awareness will only help his cause. Besides, his projectiles are unpredictable - making them challenging and fun to implement effectively for the player. When I played Olimar, I definitely felt more of a "Peach (turnips) / Pikachu (short, fast, throws self at opponent with melee attacks) / Ice Climbers (immensely technical, and partner related) / Marth (lol F-smash)" vibe, and at least 3 of those characters are fun to play! With most simple desynchs sorely missing, Olimar might be the new "Ice Climbers" - amazingly good in the right hands, but often underrepresented.
Me: Woah, my turn. So, the one thing that I checked for that I haven't seen many people worrying about is the speed of Olimar's sidestep. I main Pikachu in Melee, so I'm used to an insanely quick sidestep getting me past many of my troubles... His sidestep checks out in my book. Though it's more on the average side, I think he's earned some "so-so" moves. His sidestep seems to have average speed - it's not clunky or ridiculously fast, which probably comes as no surprise to most of you. Well SCREW YOU. I'll miss my sidestep, but I suppose it's time to move on to better things.
Alright, that's pretty much it. Unfortunately, my ability to play the game today was more of a fluke than anything, and I won't get access to the game again for another week. I will mull over any questions you have for me, but I won't be able to definitively respond until we have our UW brawl tournament in a week.