I'm just going to write shoot-em-up as "shmup" if that's fine with everybody else.
I didn't play the original PuPaiPo Space, or indeed even knew it was a game at the time, so I can't really say what the Deluxe version does that the original didn't. What I can say, however, is that PuPaiPo Space Deluxe is a solid little shmup if you just want to pop in a quarter for some arcade action.
I also have to point out that this game is adorable, with almost every enemy either being some kind of cute thing or having a cute face on it. It's my understanding that the original version had pixel graphics and the Deluxe version gives higher-definition art, and I have to say the smoother lines really added to the charm. Enemies looked impressively well-animated, too.
Being chased by a horde of chompies. I have the option to show my own hitbox enabled, which is why my character has a bit dot over them.
The game feels pretty easy, I got through Normal on my second try and Hard on my first. This is largely in part to a helpful auto-aim button in addition to manual aim-and-shoot, which helps cut a lot of the pressure out. It's not a perfect solution, since the auto-aim is a bit dumbfire and struggles against anything moving, but some clever maneuvering and knowing when to just use my cursor got around that weakness. I don't really consider the auto-aim to be a problem, since if you want a greater challenge you can just not use it, and it's an effective enough assist tool without being overpowering. I have yet to try the Ultra difficulty, but given I scraped through Hard with only a couple hits to spare even with auto-aiming, I suspect I am not going to do too well there.
There are some miscellaneous annoyances I found, however, none of which feel like they could have been hard fixes: Outside of the shield, the power-ups didn't feel very impactful, and their limited ammo didn't help. You cannot rebind your controls, which is very annoying. The game does not lock your mouse cursor into the window if you're playing in windowed mode, meaning more than a couple of times I ended up clicking on another window and having the game to out of focus - it doesn't auto-pause if this happens, by the way.
Misgivings aside, PuPaiPo Space Deluxe is a enjoyable shmup of half-hour chunks, and the mix of auto-aim and generally forgiving difficulty (easy gives you quite a few lives) would make it a nice introduction to shmups as a whole.
I enjoyed it. PuPaiPo Space Deluxe is a good game.