I picked this up last night and wound up staying up much too late.
DDU is done in a charming animated style and has you jumping from small planet to small planet searching for presents and trying to solve problems for the inhabitants all the while trying to game an understanding of "humanity" so that you don't get reprogrammed. Did I mention you're a robot? You're a robot.
This game is absolutely not going to be for everyone. There are certain triggers that have to work for you. Do you like point and click adventure games? Can you handle quirky and cute? Do you have a drive in games to complete ever growing checklists that are put before you? If you answered no to all of these, then move along. If you said yes to all of them, go get it (and know that there is a Premium bundle with more stuff).
Each planet has presents hidden for you to find. But the game gives you a button to search for hidden items. Even without that, it's really not hard to find these things. It's more like an instant reward trigger. Where it's more like a classic adventure is that most citizens have issues for you to solve. Sometimes these are fetch quests, but it's often it's about rooting through a massive inventory (which the game makes manageable) to find just the right thing for them. There's a bit of Scribblenauts here, too, as you're trying to conjure just the right object.
What makes this process satisfying is the quirky and cute nature of the universe. The characters are generally charming, and it feels nice to help them. There have been times where the 5 year old in my brain has smiled and said, "Awww." But it's rarely sickening. In fact, one time the alien who takes you around (and is deciding your fate) mpwas describing a planet filled with bunnies and he started to throw up a little. Another time i was talking to a flower who mentioned that one of her likes was fertilizer. Then she giggled when she asked if I knew what that was. She was overjoyed when I gave her a poop, by the way.
DDU is rarely challenging. It's a pleasant experience. What makes it work for me is the need to complete these tasks as they pile up. I'm a completionist, so when i get told I've done everything on a planet, it's immensely satisfying. Sometimes, to complete a task, you'll need to go to another planet, which opens up a whole other can of worms and off you go.
I haven't even mentioned the asteroids which have personality tests or the doctor who is assessing you for the robot factory. These are not scientific at all, but are still surprisingly accurate. They're also goofy and fun.
If I have any complaints, the first would be the mail system which constantly asks if you want to log into Facebook until you accidentally click yes and then back out of it, after which it assumes you do want to log into Facebook, forcing you to back out each time. It's nice (and occaisionally useful) to get mail from in-game characters, but the FB nonsense along with a few to many menus getting in and out make it a frustration. Also, sometimes to receive presents from certain characters, you have to make them mad at you. This doesn't really fit with the tone of the game, and so can be off-putting.
These are minor issues, though. I'm really enjoying it so far.
TLDR? Doki Doki Universe is a charming, quirky and overall pleasant game with a nice sense of humor and fun characters. It's easy going nature isn't going to be for everyone, but if you think it might be for you, give the demo a try.