Maybe it's just me, but Lucario feels to slow and heavy to remind me of Marth.
Okay, back to semiserious mode.
It's funny, because Lucario's a midweight, but because of his high short hop, he can perform many of Marth's old and new combos. If you think about it, he's incredibly similar to Marth.
I mean, just look at their movesets.
Fair - Combo starter. Highly spammable.
Nair - Quick high-knockback move with no landing lag. Great KO aerial.
Dair - Makes enemies fear being below Marth/Lucario. Both have extreme gimping possibilities, do a bunch of damage, although Lucario's is a bit more useful and doesn't spike. =\
Bair - HUGE range Aerial KO move.
Utilt - Sweeping motion makes a great substitute KO move if tippered if they somehow live to high %. Great Combo starter.
Ftilt - Poker. Great range and speed, mainly for poking and getting people out of your face quickly, and can be used in combos at low %, but not so much as it gets higher, because your time you spend stuck in the cooldown pose keeps you from catching up again before they can get away and regroup.
Dtilt - Poker #2. Blazingly fast, gets people out of your face like nothing else. Also both can be combo starters at low %.
Jab - Get Out Of My Face! Can make some pretty cool mixups, like Jab(-Jab)-SideB
Neutral B - Wrecks shields (AS Charge), longest ranged attack, chargeable, incredibly powerful KO move at mid-high %, quick to come out if uncharged...
Forward B - Can be chained together, VERY hard to spotdodge, great range, can be quick, messes with momentum, though Marth's is much more spammable...
Down B - Counter. Nuff Said. Marth's is a bit more useful/easier to hit with, though, while Lucario's will kill reliably. Both mess with air momentum greatly and make very good moves if done on reaction or off a prediction.
Up B - Quick as hell, but easy to edgehog. However, both are still extremely great recovery moves and are MUCH better than they first appear to the untrained eye...
Dsmash - Hits both sides (duh), deceptive range, powerful KO move, both have similar range.
Usmash - Will hit people too close to his sides, incredible duration, insane priority over air moves, similar stances, but not great KO moves in their own right until very high %s...
Fsmash - HUGE range. TIPPERS! Great spacing tool, incredible range, great duration, quick, great KO move, amazing range, all around awesome smashes.
And lastly, they both have very long disjointed hitboxes (Marth's are slightly longer, though. =\), great sweeping motions to many attacks, great range, great KO ability, can combo (Marth to a degree can still land consecutive hits and strains...), amazing aerials, but not too shabby ground games. They're both doing great in tournaments, although Marth is a bit more popular (most likely due to him being older and thus much more widely known, and the fact that he kicks *** probably helps, too), and both have very few bad matchups, but those few bad matchups are pretty darn bad.
Oshi-I got off topic again. <<
Bleh, Melee and Brawl Marth are similar enough for the same things to apply. =P