Severely under-rated, DQH seems to have crept under the radar, but it's certainly worth your time!
The music can get very repetitive so I've been playing mostly with the sound turned down, but many of the effects are cute and fit the action very well. The real unexpected part of DQH is the sense of humour displayed in the English translation, which is a brilliant example of thoughtful localisation and displays excellent personality throughout. Some of the tank names and subtitles are sheer class and whoever translated this game should be given a significant bonus and pat on the back because they've done a great job.
The structure and relationship between actions, plot revelation and expansion of locations available to explore is just about perfect, with more than one thing available to do about 95% of the time and various areas opening up at what feels like just the right point, usually when you're about to run out of meaningful things to do. The way Boingburg gradually becomes more populated with the game's personalities and reveals its charms and features as you progress is really nice and never makes you feel like you've been playing for hours and made no visible progress. There are optional collection aspects if you're that way inclined, but there is no aimless wandering here. The tank battle ranking tournament is fun and provides a good extra challenge from the top of Rank B upwards, even if most of the tank battles in the story part of the game itself are a little easy once you've sussed which ammo is best against certain enemy tanks and ammo but they certainly aren't merely a case of hurling more at your enemy than they can fire back in reply, because you can choose a team of allies to perform strategic actions against the enemy. Three allies are available at any one time, once obtained via the dungeon sections of the story mode, and abilities such as restoring hit points to your tank, loading ammunition into the canons for you, preventing enemies from entering your tank and sabotaging the enemy tank are available, among others. The tank battles make for something a little different when it comes to what are essentially boss battles, although there are a few more traditional platform game styled boss battles too, which unsurprisingly aren't very difficult to beat, but that's kind of the point of the whole game. It's to be enjoyed and the in-jokes to be savoured, rather than something that will make you swear copiously and throw your DS at the wall in frustration.
It doesn't matter at all that the game doesn't take advantage of any DS features save using the top screen as a map and menu, the game even humourously alludes to that itself with its "Nothing to see down here!" caption when you pause the game. This is a game that could easily be done on a SNES, but that's no bad thing. It reminds me a lot of Enix's best days and their 16-bit ARPGs such as Illusion of Gaia and Terranigma, in that DQH only provides a fair-to-middling amount of challenge but still has enough to keep the experienced gamer interested. I also very much appreciate that it's completable in about 15-20 hours, less if you completely ignore the few side quests available, as without some heavy variations on the formula which would probably have diluted the purity of the fun on offer, this game would have suffered from repetitiveness had it been any longer. For what it is, and what it appears they've set out to make, Square-Enix have done a great job. Dragon Quest Heroes: Rocket Slime is ace.