I've already said my part and for the most part I agree with ferrariman, but why not add a little bit more.
I've seen people mainly on GameFAQs ask why Gold/Silver deserve to be remade. The best answers I can come up with are, first game to have the two new types of Dark and Steel, 100 more original creatures as well as a few new evolves, new features like the radio, real-time clock and I think the ability to refight trainers, but I think the one thing that made the game so great was...
"Okay, so I've beaten the Elite Four, now what? Okay, Surf over here, go through this cave...oh hey, new people, huh. ...Wait. Wait, this looks familiar. ...! Oh my God. Oh my fucking God! Th-this is Kanto! Holy shit!"
You go back to the fucking first game's areas! Talk about a nostalgia power trip. A whopping sixteen badges to collect in total, as well as taking on "yourself" in Silver Cave or wherever that place was. And Red/yourself to this date has the highest level of any Trainer you can fight across the four current generations (I believe). He was like the secret impossible extra boss in your RPGs anymore, fifty billion times harder than the final boss.
All of that, and G/S didn't have that EV/IV bullshit as well as the screwy Nature system. Okay, stat randomization I can understand, but now suddenly what you fight determines what your stats are? And hey, this Pokemon doesn't have the right allocation of stats, throw it away! You can tell I wasn't one of the people who min-maxed my way through the games, huh? =P
The thing about the system that still irks me is that random battles are invisible. You don't see anything coming and without a Repel, you have no chance to avoid battle without absolutely murdering the monster or attempting to flee--and failing. Getting through any cave area is just utterly taxing because you fight Zubat and Zubat and fucking ZUBAT over and over again, and it's just irritating as hell.
And the story, I've already touched on that, but there's no depth at all. Ohnoes, the world's gunna be destroyed unless you catch superlegendaryofsometype! Oh yeah, and destroy this one world-domination group while you're at it, huh? And hey, here's a million different creatures to collect for no reason! God.
Now see, this is what I like about PMD, as I've also stated. There's a story. Hell, there's even character development that all of the past four generations have lacked! I mean, in the core games, the only people to really have personality are the bad guys, and everyone else you meet just has a couple of lines and they're through. Oh yeah, don't forget your rival, who wants to cut your throat in your sleep but doesn't love his Pokeymans enough to beat your kill-anything-that-moves team. You don't say a word, and your team, all they do is attack and die. Whoopdy-shit.
PMD has personality. Talk to people in town, they have their own personalities and demeanors. Even fighting is better than the core games. Getting attacked in eight directions in a monster house has been more nerve-wracking than anything any Trainer has thrown against me. And recruiting is the best thing ever: Kill something and it may want to join you! A lot better than "hope I don't kill the thing and waste about 20 balls trying to catch it" that we've come to know and love. And, I've come to love long-ranged combat. See an Ice-type on the other side of the room? Flamethrower and watch the ball fly over and kill. Attacks actually affect more than one thing now! Even the basic Growl will lower the attack of all enemies in a room.
Bottom line: The core series is stale and old to me. Even a fifth generation wouldn't garner enough interest in me to even download. Sorry, Nintendo.