EVen the older Retron 3 is excellent for SNES compatibility and performance. With the S-video output and a real first party SNES controller, there's literally no difference from the real hardware in any game you throw at it. It will play any SNES game with the lone exception of SA-1 games because they require a lockout chip still under patient by Nintendo and thus illegal to produce. The only game in this case that won't play that you probably would care about is Super Mario RPG: Legend of the Seven Stars. As mentioned though, it will play every other SNES game you try, including repros as Seiken Densetsu 3 and Star Fox 2 both work perfectly on it. It also plays the Super Powerpak from Retrozone. It lacks region lock tabs, so it will also play Super Famicom games perfectly as well.
The Genesis side is good too, but not as perfect. While S-video provides a clean clear video, the audio is a little wonky. Not AWFUL like AtGames attempts, it's just that the volume levels are not what they should be, meaning some of the audio is twice as loud as it should be (some background music, some sound effects) while other music that should be louder is twice as quiet as usual (some lead music). It leads you to hear some things you probably would not have noticed on a real Genesis.
The biggest problem I have with it though is the NOAC Famiclone. It's little better than a 2005 Yobo FC Game Console. Inaccurate sound, wrong colors, displays glitches on some games, doesn't play advanced stuff like Castlevania 3 or the NES Powerpak.
When you buy one, make sure you get one in a smaller box without a handle or flip top design. The newer one has the word "Retron" in blue letters, while the older has it in white. Apparently the difference is that the newer one has a better NOAC and only three settings for the dile instead of four like the original.
All this said, when buying, first make sure you buy from a seller willing to accept returns or exchanges. As you can probably imagine, this is a system from China and carries no real quality guarantee. While mine has been fine, I've heard reports of system's being broken, defective, parts not working, stereo sound being reversed, controller ports not working, etc. Not sure how much of a real concern this is, but just be ready for a plan B should the worst happen to you.
