A lot of the time, a reviewer will use one game to describe another as a kind of convenient shorthand. It's never quite accurate and it arguably does a disservice to the game being discussed, since it carries the connotation that the game doesn't have any of its own original ideas, but it's a useful abbreviation when you're working with a limited word count (or, perhaps more likely, operating on the assumption that your audience has a really limited attention span). There's no reason to burn a paragraph describing the game's mechanics when you can just say "Doom with bunnies" or "Halo with vampires" or "Left 4 Dead with mimes" or whatever, then go about the business of the review.
With 3D Dot Game Heroes, it is not as useful a descriptive shortcut as usual, because 3D Dot Game Heroes is a Legend of Zelda game. I am not saying this as a snarky comment about its real or perceived quality or as a useful way to describe its gameplay. I am saying it because it is, from start to finish, a Zelda game.
It's kind of a snapshot of a particular point in gaming history. 3DDGH is maybe one part of the first Zelda to one part A Link to the Past, with a little bit of the original Dragon Warrior laid over on the top for spice. Even the music sounds quite like the old Zelda music, and the enemies are very much in the same mold.
The joke, such as it is, is that the universe used to be 2D, but has since transformed into a three-dimensional place. Everything is made up of blocks, which shatter apart when an enemy is dispatched, and the game takes place on a 3D isometric plane. You're the descendant of a famous hero, sent out to claim an ancient sword and explore seven dungeons on a quest to save the world.
3DDGH's tongue is firmly planted in its cheek, much in the same way as the games that inspired it. Some of the NPCs seem self-consciously aware of the environment they're in, and certain aspects of the game, like your dramatically oversized sword, are on that weird knife's-edge where I'm not sure if they're intended as a parody or not. At least, I would presume that a game mechanic where my sword's blade is roughly the size of a four-door sedan is a joke, but this is From Software. They're on another plane of existence.
The gameplay itself is essentially identical to the original Legend of Zelda. You find many of the same weapons, many of the enemies behave identically, puzzles are solved in much the same way, and there's just as much of a focus on exploration. It's not quite as unforgiving as the original Zelda was, where a fresh Link in the first minutes of the game is a fragile creature made of spun glass and hope, and there are side quests everywhere. The achievements are set up to reward people who enjoy challenging themselves, the same way people used to make "swordless" runs in the original Zelda, and you can either run straight through the main game in eight to ten hours or sink dozens of hours into the various side quests.
The original Legend of Zelda and A Link to the Past are classics for a variety of good reasons, and both still hold up fairly well today. The easiest way to view 3D Dot Game Heroes is as an unofficial, vaguely next-gen sequel in that series, and in that light, it comes off really well. You could do a whole lot worse than being a lot like a couple of the best adventure games of all time.
The flipside is that if it were a Zelda game, it would be an unexciting, safe game that displays a troubling lack of innovation. It copies most of its gameplay and doesn't really do anything of its own.
If you were a huge Zelda nerd as a kid, or if you still are, this is probably going to be a complete and welcome nostalgia trip for you. I was more of a Mega Man guy back in the day, so 3D Dot Game Heroes doesn't really do much for me. It's more of a flashback than anything else, and relies too much on your affection for older games.