Me and my fiancé spent some quality time on this during the weekend, playing 5 matches of 10 or 15 rounds each, us 2 and 2 CPUs. Here's my considerations so far, from someone who probably last played a Mario Party game around the DS times and even then briefly, so I really have no way to compare to much that the series had before, and I'm not going therefore to talk about how the boards feel smaller or anything.
First of all, I think the boards are fine. What appears initially very straight-forward can become really bonkers (the one with the tropical islands is mad), but the fact there isn't some groundshaking event every 2 steps makes it easier to strategize. Of course, you can only calculate things to a certain point, as there are cases (on the islands again, in particular) when you need very specific drops, and of course the star moves to random locations which can screw people over drastically, but hey, that's Mario Party for you. I'm slightly disappointed that the endgame of each is the same, in the sense that the last 3 turns get everything doubled basically, with an unskippable cutscene to announce so every time. As we progressed through the boards it became kinda annoying to watch it for the 4th and 5th time. Special mention to the golden board at the end: straight-forward, tactical, very fun overall, really enjoyed the wager mechanism and the shortcuts on there.
Let's talk about the minigames then, shall we? They're pretty good. There are a few which are close to unplayable with CPUs on your side and a human on the other because they require some oddly specific skills the computer seems to lack (on lower difficulties, that is), but overall I feel like the minigames offer more than enough value and variety. Out of the 80 there are still many I haven't seen. Some have really excellent background and surroundings as well, plus I'm surprised how non-invasive the motion controls feel most of the times: one thing I hated about the Wii era, for example, is how basically every Nintendo game decided to assign some pretty important move to a relatively complex motion-based event rather than use a damn button. I didn't find that to be the case here, even if throwing the dice does in fact require a movement.
We only played general Mario Party rules so far, enough to get a Gold on each of the 4 boards. There have been many of the Mario Party shenanigans (random stars gifted to people to turn the match around its head is a classic, for better or worse), and in most matches it felt like there was always a superlucky player and a very unlucky one, be that human or CPU. For reference, I had a match where I ended up dead last with one star despite playing well, and another 15 rounds match where I finished with EIGHT stars (and it wasn't even the golden board which showers you with stars). The game's randomness makes it more exciting but it can be slightly frustrating at times, but for example it was hilarious to go through the golden board as we were calculating the paths, the throws, the power-ups required to get another run at buying stars, and how that will manipulate the results of the game. Fun stuff.
We yet have to try the other game modes, as we only unlocked the first gem given for the Mario Party mode specifically. What we played so far has been mostly really great, and while I would have enjoyed more tables, I don't feel like I wasted my money or anything, as we'll still play this quite some hours probably. The power-ups, the different dices and such make for a decent variety of how the matches go. Perhaps the ally mechanism is slightly OP, as there seems to be way too many advantages for owning a buddy. That one match I ended with 8 stars? Happened when I had 3 buddies by my side. I could basically move wherever I wanted. In that sense maybe the smallish boards can be an issue, but I've only really found "problems" with the small paths on the islands, and there you can kinda need to land on 2 specific locations to get out anyway once the bridges go down, so may as well have the isles small indeed.
Overall, I think this is a good game, a fine addition to my library of Switch games that will make for an excellent travelling buddy as well, since we can just place the screen on the table and duke it out with the Joy-Cons - it usually isn't even that awkward with there being relatively few heavy motion-based activities to boot. That would probably have us play with no or limited volume, which would make another feature shine: the fact that the current player's Joy-Con plays a little jingle with the vibration is genius, I've hard mine like 50 times already and I can't get enough of it, lol. I may play some more later today, we'll see, either way it seems like an excellent entry point for a Mario Party. I do hope they will add more free tables, characters and minigames, but as is the game is fun and enjoyable for the most part.