The first 5 games had really great minigames, with 3 in particular having some of the best in the series. 6 through 8 not so much, which is a shame because I love Mario Party 6 and 7's boards but a lot of their minigames bore me. I've always considered 4 & 5 to be the opposite of 6 & 7, the first two have great minigames but I'm not a big fan of their boards and the gameplay is so slow because the characters move around the board at a snail's pace. 6 and 7 have faster board gameplay and great boards, but don't like the minigames.
As for soundtracks, I sometimes listen to the Gamecube MP's soundtracks, but I dunno...The newer games' music sounds cuter, more catchy, and more Mario-like I guess?
I actually don't like the N64 minigames as much, as a portion of them rely on rapid memory skills, something I struggle with and is a big reason I got scared off playing Mario Party at an early age. I always get anxiety at Messy Memory and The Beat Goes On, which I don't get the same feeling playing, like, Memory Lane though I keep losing to my sister in Memory Lane. They're home to some of the worst dreck of I've played including Honeycomb Havoc (MP2), Cast Aways (MP1), Toadstool Titan (MP3), Crane Game (MP2), Rockin' Raceway (MP3), Bash N Cash (MP1), Bowl Over (MP1/MP2), Piranha's Pursuit (MP1; the team has nearly no chance of winning if the sole player can clear these easily-dodged rocks); whereas some minigames I always thought were done better in later installments (Hide and Go Boom is way more hilarious than Hide and Sneak). Sure, Mario Party 6 has Same is Lame, Treasure Trawlers, and Trap Ease Artist but IMO their minigames are quite solid having games like Lift Leapers, Cannonball Fun, Snow Brawl, Snow Whirled, Rocky Road, Granite Getaway, Clean Team.
I also think 5's speed is reasonable, but I was pretty surprised going into N64 Mario Party after being so accustomed to move speeds in GCN games, especially Mario Party 4's speeds, how fast these people move and hit a space. Like... wow they don't even react when landing on a red space.
Eh for soundtrack I like em all, mostly from exposure. I've taken a liking to the modern ones too, though they do have that... style. Like it's more heavy on xylophones, synth, and whatnot. I like the harpsichord/keyboard music in Mario Party 5 or that one. Mario Party 2 I just know the sax from
Keepin On Path (which Mario Party Superstars really dialed back and made it just a background note; what a disappointment).
Amusing from Mario Party 6 sounds sufficiently Mario to me... Mario Party 6 sounds way louder to me, has significantly more brass; same for Mario Party 7. Mario Party 4 has a lot of synth, more than the other GCN Mario Parties. They're all different to me, maybe 6 and 7 sounding most alike to each other. I find it harder to pick out tracks from 10 and like Star Rush due to both having huge use of xylophone, but it could just be less exposure. Anyhow, I grew up with the sax, brass, and whatnot, not really the xylophones.
The Mario Party 10 music sound definitely more reliant "synth" and "digitized" to me than the GCN ones imo. Compare
Exciting and Exciting (10) to like
Exciting Walk (5), which have similar moods but one is really synth heavy (despite having prominent flute and clarinets, but the synth is still first and foremost), the other has more brass, bassoon (?) wood block noises(?) xylophones, sax, and harpischord.