Videogame Remakes: Good or bad?

Y'all know that my gaming involves MOSTLY retro games and I tend to stay at most one Generation behind the current Generation. I tend to blame Square Enix Sucking and the abundance of Generic FPS game # 769 now with Zombies because Zombies are cool!

So, I've been looking at old school games once again... (32Bits and lower) because anything fancier tends to be an HD Port of (Insert game here) with maybe some features that were cut out of the less powerful console. In some cases, we get lazy ass ports of a PS1 game for PS4.

Recently, I was able to borrow a copy of Metroid: Zero Mission and Super Castlevania IV...
The common trend on both of these games are that they are a Remake of an Original NES Game.
Metroid and Castlevania, respectively. I also I'm the proud owner of a copy of MGS: The Twin Snakes, which is a remake of Metal Gear Solid...

Can you guess what these three games have in common? Aside that they are remakes.
They are remakes with extra gameplay features that the Original lacked that make these games feel familiar but different! It goes beyond a simple Graphics update and refreshes the classic game. At the same time, I fear too many rehashes of the same game can become annoying... Isn't that right Capcom and your multiple RE-Makes of RE1... (I could count the Original RE-Make) Don't get me started on Street Fighter II! (I love SFII, but that game has been remade and ported so many times that if you fart on any direction, the flatus may reach a SFII Port.)
Now the reason I make an emphasis in Extra Gameplay Features is because some companies tend to do ports and give them some new cutscenes and expect us to think! Oooh! Wow! a Remake!

Not saying any names here...

Sometimes, these remakes tend to correct something tedious from the previous version, but in some cases, the remake may have some better things than the original (Extra missions, playable characters, translation errors corrected, fixed bugs/glitches) but end up being inferior due to some issues... Massive slowdown when doing some flashy attacks...

So here's the question: Are Remakes good or bad?
I have to say that this is a loaded question and could only be answered on a case by case scenario.
The only reason I enjoy some of these remakes is BECAUSE I've played the Original (Truth be told: I never beat the original Metroid, but was able to beat Zero Mission.) Also, there are plenty of games that DESERVE a Remake, if it's just to tell the story a bit better and "complete the circle" (MG, and MG2:SS I'm looking at you.)