Despite being a big fan of Old School RPGs, Dragon Quest was never one of them for me. There are a few entries I like, but despite being one of the staples of the genre I just never could fully get behind it as a whole. Of the games in the series I enjoy, one of them was IX on the 3DS.
Playing the role of a celestial being, it is your duty to gather the goodwill of the people you watch over (Which takes the form of Benevolesence), and return it to the sky so that one day you will be able to go to the realm of the Almighty. The idea is that the more you help people, the more you can gather. That said, this portion of the story doesn't last long as you reach the goal before the meat of the game kicks in. Instead, as the sky opens, lightning strikes down the starlight express and sends you back down to the mortal realm, where you seem to be human now. From here the main plot becomes about finding your way home, learning what happened, and the story behind the fallen Celestian Corvus.
While I said I like this game, it is not because the main plot is good. Frankly, none of it is even all that interesting. Dragon Quest has never been a game where the main plot has been all that interesting, so this is nothing new, but here it seems lackluster even by series standards. But, also like other entries, there are portions of the game and small story arcs that are interesting. Part of the plot, for example, has you looking for Figs that fell from the World Tree, and people who eat them have their desires granted and corrupted. A few of these are pretty lame, like Swinedipple Academy where the ghost of a teacher wishes to guide the students, and instead starts kidnapping them and forcing them to study. One of the more interesting ones involves the doll of a deceased girl coming to life, and it's kind of heartbreaking and beautiful. A lot of interesting ideas and a lot of boring ideas, especially once the main plot kicks back into gear.
That said, I don't think the story or characters are worth talking about. Your party consists of you and four NPCs that you also customize. Class, skill points, visuals, all things you decide upon yourself. From a story perspective, this is kind of lame, but from a gameplay perspective, it's where the game becomes a lot of fun. Your level resets back to one when you chance class (Though if you change back you go to the level you were at that class). However, any points invested remain invested, and any unspent remain available to use. Each class has a passive ability where you gain passive stat buffs as well as abilities that can be used regardless of class or gear. You can also invest in weapon skills that are only usable while equipped with the proper gear. While classes only have the specific gear they can equip, maxing out a weapon tree allows for you to equip that weapon regardless of class.
I do dislike how certain classes are not very good, and so. The most obvious being Minstrel. You have a few classes where you will only get a few early levels in it for some easy points to use elsewhere (Or maybe for one specific ability like the Thiefs Half Inch). It has always bothered me in games that include classes like this have some options that are just so obviously bad you wonder why it would have been put into the game in the first place.
With customization out of the way, it's just another Dragon Quest Game in terms of the game-play. Basic Turn-based comments, the addition of Coup de graces is nice, a mechanic where each class can build up to a unique move of some kind, but it doesn't add a whole lot of depth to the system. Of course, it is Dragon Quest, the series is pretty famous for keeping the same old-school feel to its mechanics, and it does a good job with it here. If you're like me and have always been indifferent to most Dragon Quest games, you may end up enjoying it. If you actively dislike DQ at all, this game will do nothing to win you over.
Sentinels of the Starry Sky I think is just a good game overall. Fun short story arcs, solid combat, and a lot of customization. It does suffer from having a boring main plot, which starts to become an issue when the shorter story arcs stop being a thing, and if you've played a lot of RPGs before there isn't a whole lot here to freshen up the experience. If you already have an idea of what you think about this series as a whole you'll probably already know how you'll feel going into this, but if you are interested in getting into the series for the first time it's a good place to start.
Note: I wasn't thinking of a review when I played back through it, so I didn't grab any screenshots. All Screenshots come from various Dragon Quest Wiki's.