Played through the demo and I'd say what's there so far seems quite promising. It's only one town and route each so not really enough to form concrete expectations; the starting town doesn't have much going on as is usual for Pokémon games but Route 1 has an interesting little gimmick to it that's required to progress through the first time.
Regarding the plot there's not mucbh that can be said since the demo barely scratched the surface but the setup seems interesting enough, although I think the intro bit of the game brings up the bit about your parents a little too often in quick succession. Otherwise the only thing I can say is that I'm not really sure what Aria being a character from the anime is intended to contribute; it seems to be mostly just used as a backstory for her although as someone who hasn't watched the Pokémon anime in a hot minute I don't know what sort of reaction I'm supposed to have to her presence. It did kinda bug me how she just ditches her old Pokémon now because reasons when it's her explicit motivation to become able to protect herself and her family so sticking with the Pokémon she already knows for a long time and is familiar with should really be the smarter choice.
Visually the game looks nice so far. Gen IV graphics produce pretty clean environments and it works well for Route 1 and Goldsong Village's coast. The custom NPC sprites blend in well and the one we get to see in battle so far looks quite good. The protgaonist's various sprites unfortunately all look rather plain and uninteresting, particularly the male ones.
There are no major battles in this demo, but the random trainers on Route 1 are unfortunately rather ill-balanced in my opinion. There levels are a little too high for how little exp you can get until that point without grinding wild encounters and they use quite a number of Pokémon species that are just too strong for that point in the game. The second trainer you can find on Route 1 has a Durant, a Pokémon with three base stats higher than 100 at a point where players are lucky to have more than two Pokémon above Level 5 without grinding them out. Other standout Pokémon found on Route 1 include a Sudowoodo with Stone Edge, a Minimize spamming Litwick that's also surprisingly tanky, a Draining Kiss spamming Comfey that's annoyingly tanky, a Wigglytuff with Hyper Voice, a Snubbul with Elemental Fangs for coverage and potentially an ability that sharply raises its Speed, a Sneasel and a Dunsparce that will Rollout you into oblivion if you don't get rid of it quickly. With a lot of annoyingly strong enemies running around much of the gameplay is spend progressing a few stept forward and then immediately turning back around to the Nurse at the entrance to the Route because your team is on its last leg after just one, maybe two trainer battles. Many of the trainers also already carry three or four Pokémon with them with can make breaking through some of those annoyingly strong ones even more of an issue.
Another contributing factor is that the early game seems rather heavily skewed in favor of Fire Type Starters and pretty heavily screwing over the other two Types. With Route 2 being set in a forest some Type bias is expected but it becomes kind of an issue when the trainers get in on it as well. The Field boosts Grass moves but many of the enemies resist it so if your Starter is a Grass Type your strongest team member's offense just got screwed while Water Starters need to be wary of enemies' powered up Grass moves. Fire Types meanwhile get to burn through the plentiful Bugs you have to fight on this route while being threatened by relatively few enemies.
All that is exacerbated by battles being locked to "Set" mode. I get that it's a game design choice to make battles more challenging by removing a player-only advantage but it really never improves anything when it's forced on everyone. The vast majority of the time all it does is make random trainers more time-consuming to beat than they should be and training up new team members harder than it needs to be. Even if you feel like Set mode is somehow an absolutely vital component for the game to be fun and challenging I feel it would be a much better idea to restrict them to fights where it actually matters instead of also extending it to those trainers that should mainly exist to feed us exp on our way between the important bits of the game. Also options really don't hurt anybody.
Random bit about music: I ran itno an Aroma Lady using Hopes and Dreams from Undertale for her battle music and then a few stept further an Dancer who used a track ripped straight from I think the Gen II games. Talk about whiplash. Also personal opinion but I feel like you shouldn't use climactic final boss music on random route trainers because it dulls the impact of whatever track you'll be using for the battles that are actually supposed to feel climactic. Particularly if it's music from other games the emotional connection players may have with it is going to make it hard for other tracks to compete against that.
Lastly two bugs I encountered: during the battle at the big honey tree the enemy's Lv 6 Combee had an invisible sprite
Secondly both Fury Swipes and Fury Attack don't work and throw out an error related to the Battlebond Ability for some unfathomable reason:
Clicking on OK results in the Pokémon's turn being skipped