I got mine today
I've played around with it for a bit, so here are some of my initial impressions...
First, let's cover general things that currently Just Don't Work (as far as I can tell).1. Repro and homebrew carts. I've got a few of these, all from the same place, all NES, and they're all ones that use original parts and semi-clear cartridge housing. Nintendo World Championships 1990, Mr. Gimmick, and the two Battle Kid games. Any time I put one in, the Retron 5 insisted that no cartridge was even inserted.
Hyperkin have stated that they want to support homebrew developers in the future and will be releasing firmware updates to do so, but there are not any firmware updates available yet as of this post.
2. Maybe multicarts? I have a Chinese 76 in 1 Famicom cart that also gives the "no cartridge" message. It may just need to be cleaned. I'll post any update on that later.
3. The various NES, SNES, Genesis flashcarts. I don't have these to test, but the word from Hyperkin is they don't work. (A little more on this in the next section)
Things that do work that surprised me.1. A GBA flashcart with only one rom on it and no menu. So, I've got an "EFA-LINKER" GBA flashcart that I've had for ages, and last time I every bothered with it I put only the English translation for Mother 3 on it, and told it to load straight to that and bypass its menu. I put that in the Retron 5, and it surprisingly works perfectly well. It pulls up as an unrecognized game, and complains about it, but I really didn't expect it to work at all. Flashcarts aren't supposed to work on the Retron 5, and I believe that's because it only sees and dumps the flashcarts menu. So... If you've got a flashcart that can load a single rom without a menu and don't mind the hassle of putting a different game onto it every time... You're good?
2. Super Nintendo Mouse. Not that it worked at all, I expected it would with the games that supported it (I've tried both Mario Paint and Arkanoid-Doh it Again), but that it can be used to navigate the system's menus! As in, a little mouse cursor appears and you can click around through the options. It's a neat extra.
Famicom specifics.This is the only system that I've tried everything I have, and about half of my small collection of carts worked. The others might need cleaning, but I'll talk about them anyway
The 76-in-1 I mentioned earlier and my copy of Salamander both just didn't show up at all. "No cartridge"
My two Konami Famicom games: Crisis Force and Akumajou Special: Boku Dracula-kun (AKA Kid Dracula) both gave a Bad Dump Error.
Some of the ones that did work took a little fiddling on the positioning (CluClu Land in particular), but again, I may simply need to clean them.
NES specifics.I didn't try much beyond my repros here. The couple regular carts I tried worked, as did unlicensed (Tengen) ones. I did not try the Game Genie, but I suspect it would not work (but there's codes built into the system so whatever)
SNES specifics.Like I said before, the SNES mouse works fine.
Regular SNES games work fine, as do Super Famicom games.
The Super Gameboy does not work. The Retron 5 recognizes it, and will boot it up, but all you get is the Gameboy frame with a black center. Not a big loss for the most part, since it plays GB games already, but... more on that in the Gameboy section.
Genesis specifics.Regular Genesis games work alright, as do Master System games through the Power Base Converter.
The Power Base Converter does not sit as flush as I'd like. The cartridge slot isn't as deep as the one on a model 1 Genesis, so the Converter sticks out a bit and is kind of wobbly.
The only Mega Drive game I have to test, Zero Wing (PAL), pulled up as unrecognized and froze on the SEGA logo. Again, I may simply need to clean it.
Most notably, Sonic & Knuckles' pass-through functionality does not work. No Knuckles in Sonic 2, no Sonic 3 & Knuckles. The Retron 5 always simply pulls it up as Sonic & Knuckles. I hope they can fix this in a firmware update.
I did not try my Genesis Game Genie, but I also expect it to not work (but there's codes built into the system so whatever)
Gameboy family specifics.Gameboy Advance games run basically as you'd expect.
Gameboy Color and Gameboy games have a small problem with their display. Annoyingly, the whole display seems to be rendered one pixel lower than it should, cutting off the very bottom row and rendering a solid black line above the top. This might not matter for most games, but some have text that is supposed to extend all the way onto the bottom. Check out this screenshot I took on the system of Wario Land 3:
See how the letter y is cut off on the bottom? This should be fixed in a firmware update, but it's annoying for now.
UPDATE: I've informed Hyperkin of this issue, and they've got it fixed in the current development build, so the first firmware update should fix it 
Other than that...
Gameboy Color games render exactly as you'd expect, both the clear GBC-only ones and the black GBC-or-GB ones.
Gameboy games with Super Gameboy enhancements render with their SGB colors, but for whatever reason the SGB borders aren't utilized at all. I would have expected them to at least be displayed on the left/right side of the game, but nope; just black.
Regular Gameboy games with no SGB enhancements run in a basic 4-shades-of-gray monochrome. Some other color choices would have been nice, like the ones from playing one of these games on a GBC... But nope. Just gray.
As for specific game stuff...
WarioWare Twisted loads up fine, but even if you wanted to try twisting your Retron 5 around, it can't seem to communicate with the sensor in the cart. Sorry =P
Kirby's Tilt 'n Tumble and Gameboy camera both fail to dump, presumably because of their extra hardware.
Pokemon Pinball (GBC) worked fine. Didn't have a AAA battery to put in to see if it rumbled, but I suspect it won't.
General impressions.The plastic feels cheap. It has a death grip on the carts that's somewhat common on these clone systems, but you want to be careful not to push on the surrounding cart ports as that plastic actually bowed in when I did so.
The wireless controller... Is not completely worthless, but it's not super comfortable. The click stick, which is similar to the one on the NeoGeo, doesn't work as well as a d-pad in some games, but works perfectly fine (perhaps better) for others (like shmups). The buttons are all microswitch-based, so they're very clicky. The default button mapping on the thing is weird, too. + and - default to B and A on the NES, but the system menu uses + as confirm and - as back. On the SNES, instead of using the four arrow buttons like I expected, it uses +, -, < and V and ignored ^ and >. Of course, the buttons it uses for what on each system can be remapped, but it will still use + and - as confirm and back on the menus, which just feels backwards for where they're placed. On the whole, I recommend the original system controllers if you've got them.
Speaking of buttons and such, you can map the various extra features to different button combinations for each controller in the system menu. For example, bringing up the system menu in game defaults to down+start on all the controllers. I did run into one of these mappings accidentally: up+a+b on the NES controller is by default mapped to fast forward, which I triggered while playing Super Mario Land 2 running along and then jumping up into a pipe while still holding run. Remapping it was easy, and I mapped it to up+a+b+select instead.
Also, as you can tell by the above Wario Land 3 screenshot, the screenshot function produces images with some terrible jpeg artifacting
That's everything I can think of at the moment. If anyone has any specific questions, just ask.
