Played several times on Normal and Hard covering most shot types. As you've been told already, congratulations on contributing more quality content to the Summer of Fangames! Here's my assorted thoughts.
I can definitely tell this is a sequel to TSS - aside from the obvious returning characters and stuff, there's something about the danmaku design that feels similar to that game. I can't quite put it into words, but it's neat to see specific styles evolving among fangame developers. Something else SoHW shares with its predecessor is a fairly high difficulty. I'm completely fine with that this time around, since it's not cranked up as high as TSS, where Normal almost felt more like Hard.
It's really fun to try and gather as many harvest items as I can during the Harvest Event, and the orange indicator that turns green once I've filled the harvest quota is a great touch. I felt the vortexes from TSS could've used clearer indicators; the only way to tell how close you are to spawning life/bomb pieces is to look way over to the HUD on the right, which isn't optimal when you're trying to stay on the vortex and simultaneously dodge stuff coming at you. And while this is fairly minor, I thought there should've been some little visual effect to represent your character sucking in the vortex. Both of these complaints have been fixed with the Harvest system, so excellent job on that.
One fairly significant gripe I have with SoHW's system, however, is that the PoC seems to work the way it did in earlier Touhou games - going above the PoC and then heading back down while the items are still flying toward you will make them worth less than their full value. They're worth the correct full value if auto-collected during a Harvest Event, so if you guys want to fix this I imagine it wouldn't be hard.
Aside from the fact that Ryouko is a cinnamon bun and fun to play as, it's just really cool to see an original character being promoted to playable. I'm honestly surprised I haven't seen more fangames do that; I think Tobiko in Tri Focuser is the only other example I can think of? (While I'm here, combining the character and shot type selections into a single menu is a neat idea.) Yukiko being a retired incident-causer is also an awesome concept I don't think I've seen before. The first three stages didn't reveal too much about the story, so I don't have a lot to say other than I'm looking forward to seeing how it turns out. The dialogue felt sort of weird to me, but I know that's the case in plenty of Touhou games so I guess it isn't a big deal. I enjoyed a few lines like Marisa's "I've seen fairies last longer than this" and Kagemo's "Die."
In terms of music tracks, all of them are good. Yukiko's theme and the theme of her stage are some of my favorite songs so far. I presume the title "Beware the Forest's Flowers" is an intentional nod to Super Mario RPG? Nice. The first stage theme, while I'm not sure if I'd say it's one of the best, is really fitting for the seriousness of the incident. The title screen music is another favorite. I adore the melody that kicks in at 0:13. It sounds melancholy but at the same time optimistic, like "This is a serious incident and people could starve, so let's get out there and put a stop to this!"
While SoHW is nowhere near as lag-inducing for me as TSS, it seems I still get moderate FPS drops (down to around 50) when bosses first declare spell cards and on a few patterns, particularly Yukiko's on higher difficulties, even with all effects on their lowest settings. It might just be me and my 7-years-old laptop, but I figured I'd report it. I also get lots of lag on the pause menu, but I know that's been pointed out already.
One more little touch I love is how the game tells you when you've gotten a no-miss or no-bomb clear. Just a nice little acknowledgement of the challenges fans set for themselves.
Here's a few minor bug reports and fixes I'd suggest for improvement. Some might feel nitpicky, but if I nitpick something it's because I like it and don't want even small flaws holding it back!
?Holding Z to skip through dialogue should go faster.
?Confirming a selection in the stage practice menu plays the "cancel" sound effect rather than the "confirm" one, which is pretty weird.
?The view replay and player data menus feel rather empty. The replay menu is missing the time, character/type, stage, and slowdown percentage. Player data is missing the player's name, date/time, stage, and slowdown percentage (I'm not sure if Danmakufu makes it possible to display slowdown percentage on player data, but I know it's possible on replays).
?Relatedly, high scores for game mode and stage/spell practice mode aren't stored seperately. Getting a score in either practice mode will make it show up in Player Data, and the high score will be shown as such when you play the game regardless of what mode. The menu for selecting a stage to practice should also display the high score for that stage.
?The game doesn't save the player's name, so you have to type it in every time you save a replay (you also can't attach a name to high scores).
?Practicing a stage and then selecting Return to Title sends you all the way back to the title screen; it should just take you back to the stage selection.
?Dialogue (especially after defeating a boss) should cause all items to be auto-collected.
Wishing everyone the best for development of the full game, and I'm looking forward to it!