First off, they're ARPG's, not Musou games. Some characters play like Musou characters, and you still end up killing a lot of enemies in these games, but aside from those similarities, there's way more RPG DNA here (there's skilltrees, equipment, an emphasis on sidequests, classes in the sequel etc.)
As for the specific games, Dragon Quest Heroes 1 is okay. It weirdly emphasizes this style of tower defense gameplay where you kill enemies, pick up their "Monster Medals", and then summon those defeated enemies to help you protect the specific MacGuffin in each level. Except for a few rare missions and the occasional bossfight, the entire game is just these skirmishes (and you just fly to each of these directly in your ship).
The game is all combat, and the actual combat can be very frustrating. Enemies are intentionally very annoying and time-wastey, harder missions often just require trial and error also, your party member's AI is really stupid and to top it off, you don't get a healer for most of the game (gotta pay out that Nun for health potions). Most sidequests aren't much better, with there being a lot of 'kill 100 of this specific recolour of this specific enemy". For me, all of the charm was from the story, the characters and the general presentation of the game. It's not my favourite tbh, but some people prefer it over the sequel.
Dragon Quest Heroes 2 vastly improves the gameplay. You can now change the MC's weapons and classes, you get a main hub that connects to a semi-open world that's all inter-connected (but not fully unlocked off the bat), there's less annoying tower defense / protect MacGuffin missions. And you get *healers* in this game (healers, as in plural). It doesn't sound like much, but DQH1 is so worse off for having only 1 healer (unlocked late into the game). In DQH2, as long as you have at least 2 healers, even the braindead AI will know to heal you.
The game's not perfect. The semi-open world isn't greatest (the open world lazily populates enemy encounters in the open world and the world isn't really used in missions). There's a lot of esoteric mechanics like magic damage, tag tricks, parries, reflects and proficiency (which is like a second skill tree that requires you to manually use characters and constantly talk to the Martial Artist in Town). There's also one lategame section that is the most painfully *obvious* padding ever (you'll know it when you see it). Additionally, while the game has a solidly paced campaign, the postgame / platinum is one large, awful, RNG-filled grind.
Despite some problems, I honestly feel Dragon Quest Heroes 2 is a really underrated ARPG. The campaign is a fun 20-30 hour romp (length is depending on whether you pick up any sidequests, do any grinding or have to retry missions). I believe there is a Switch version of the game that actually added an extra playable character, but I'm unsure if it left Japan. (Also make sure to tweak your options for the camera and Coup de Grace cutscenes)
