y'know what I've followed Hello's games since Mario Editor and I have seen all his 3D games and I also play hours of Isekai Mario for this. might as well list some of the problems I noticed in this game:
1. The gameplay is SM64 and Sunshine's levels and the lack of permanent power ups, combined with 3D Land and World's moveset. All 3D Mario games have a sort of alternate attack like 64's punch, Sunshine's F.L.U.D.D., Galaxy's Spin and even 3D Land and World's permanent powerups. They are made for the fact jumping on goombas in 3D is much harder than in 2D so the lack of an alternate attack in Isekai Mario feels really limiting as in some cases punching an enemy would be more preferable than jumping.
2. This might be nothing for someone but I personally really feel that the animations can be fixed to allow ending early as when the player lands on the ground moving, they end up doing the landing animation while moving which looks like they're sliding around before the animation ends and they return to the running animation. Personally I think this is a really jarring issue but I understand if others think its unimportant.
3. Physics. They are not that good. Mario feels sluggish moving and he slides around like butter on ice. jumps feel floaty and generally physics don't feel good. Also, boxes. they suck. Mario will slip off the side of the box while pushing and I recommend allowing Mario to "grab" the box and push, locking his movement to only pushing or even pulling which allows you to not get boxes stuck in corners unless you push the reset switch.
4. this actually applies to alot of fangames too. let me see the status of my file in the title screen. As a person who doesn't always use file A, its pretty annoying if you can't see a preview of your stats like stars and coins in the title screen especially since this game's title screen barely has anything going on. This actually is a pretty small problem but I would really appreciate it. Might as well mention I feel like the lighting in this game can be quite bright bc of bloom which once again is jarring but its nothing bad.
frankly, This game is actually pretty decent and can be good. 3D Mario fan games are genuinely a treat to see but if it wasn't for some glaring issues (1-3 at least) it would be at least a fun Mario game.
I'll say this much tho the character models feel lifeless so I only collect them and never use them.