Depends on the game.  I mean something like RE2 aged horribly, especially the controls, thus it needs to be rebuilt.  Something like Prime aged wonderfully so it only needed upgrades.  So it depends on the game.  

It's a case-by-case basis.
I'd like to see Paper Mario: The Thousand Year Door with an up-conversion of the resolution, but little changes to the gameplay or art style.
The original Paper Mario needs a graphical remake to match TTYD, and some gameplay aspects should be changed, like adding a post-game option after the final boss.
Many sixth-generation games and onward only need up resolutions or graphical remakes in my mind. Typically, not much of the gameplay has to be changed.

Metroid Prime Remastered is not a remake and it was never supposed to be one. It's as the name says a remaster, so expecting or wanting it to do anything different in terms of gameplay and structure is rather foolish.

Who said I expected anything different?

I haven't played either yet. But I bought Metroid Prime Remastered. It should show up at my house by Thursday. I have no plans to buy the new Resident Evil 4 remake. Actually, I just bought a digital copy of Resident Evil 4 Wii Edition when it went on sale for 3 bucks in the Wii U eshop before it shut down. So now I have 3 copies of Resident Evil 4: the original GameCube copy, a physical Wii copy, and a digital copy on my Wii U. I just haven't been too impressed by the changes I have seen with the new version of the game. There is a good chance I never pick it up.

Resident Evil 4 is my 6th favorite game of all time. Beat it on the GCN, PS2, Wii (3x) xbox HD version. The new remake looks amazing, but im not sure if I want to play it.

Well you called it a remake and said remakes should do something different.

I guess I'm more of a remaster guy. I really like the way they remade Resident Evil 1. Also stuff like Link's Awakening on Switch, Crisis Core, Asha in Monster World, and the FInal Fantasy X remaster. Essentially the same game, but with completely overhauled visuals and a few gameplay tweaks but nothing major. Something really charming about that to me.

I prefer Remasters or light Remakes - that is, either just visually enhanced original or a remade game that sticks to the original as close as possible.

Reimagings can turn out to be good games on their own, but they are quite often too far from the originals to be even considered directly connected to them, except as an inspiration.

Oh, I forgot about Link's Awakening.  I bought that one and really like it.