Apologies for the wall of text but I've a lot to say ^.^
Remasters properly done are great in my book. But only if they are actually remasters and not a quick hatchet job to print a bit more money.
The Last of Us and Resident Evil ones are two good examples for me.
You mean a remake? By my definition, a remaster is the effective porting and upgrading of performance/graphical fidelity of a game onto a newer system. A remake is something more, where they actually change the game and add things to it. That said, there can be remasters with minor additions like the LoZ: Wind Waker, which added the fast sail, previously not possible due to hardware restrictions. A remake is more like Metroid: Zero Mission (remake of original Metroid), where actual new stuff is added but the base skeleton of the game remains. Or that's how I see it at least. According to Wikipedia, everything is a remake, including Resident Evil and The Last of Us.
I will say this, one thing these remasters are good for is to increase the accessibility of the game. People may own a platform to play on games now, when they previously might not have. An example is The Last of Us. A lot of people didn't own a PS3 and didn't get to play that game, a PS4 release has allowed those people to play it. Similarly, I never played the original Legend of Zelda: Wind Waker on the Gamecube, so I enjoyed the experience of playing the HD improved version on the WiiU. In essence, these remasters can be described as ports. I was able to play MGS2, MGS3 and MGS

W on the 360 due to the MGS HD collection, when most of those games aren't normally available on that platform.
But it does come down to the accusation of a lazy cash grab. Remasters of games released within the last 5 years are unnecessary in my opinion, since those games haven't aged enough to warrant significant change in a new version. Especially with the new systems (excluding WiiU), where the remakes are an alternative to the lack of backwards compatibility. They wouldn't need a remaster of the Last of Us or Halo if those consoles played the last gen games, even just downloadable versions. But they re-release recent games and gouge full price for it. I say this: I'd honestly be willing to buy a PS4 if they made an MGS4 remake (won't ever happen). But instead I bought a cheap second-hand PS3 to play those games I missed out on, instead of buying a more expensive PS4 which doesn't have new games (exclusives to interest me). In that respect, Nintendo have it good, people can buy the older games for relatively cheap (but still overpriced

) as virtual console titles to play on current systems. Even if their implementation is flawed, at least there's no need for unnecessary remakes. The exception to this is Gamecube, when will they release GC on VC? I wanna play Melee!
I for one, hate remasters/barebones remakes in general. If it's bundling together multiple games for the price of one, then I can accept it. I enjoyed Metroid Prime Trilogy on Wii (having not played those games beforehand) and the MGS HD collection on the X360. But my exception is Halo MCC.
I was very disappointed with the Halo Anniversary remasters. They half defeated the point of a remake/remaster and kept the original graphics. Considering that people can still play the original Halo, either by the old PC version or by putting the original Xbox game into an X360 (or even buying it as a download?), there was no point to this terrible gimmick. As a ex-fan of Halo, I often wondered what it would be like if they solved the continuity of the games and added the newer weapons/equipment/enemies into the older games. Reach had Spartan lasers, but they were absent in Halo1/2 before appearing in Halo 3. I remember playing a modded level of Halo 1 where there was the addition of Halo 2 weapons. Heck, some things like plasma swords, fuel rod cannons and Wraiths were already in the game, it was just that players couldn't use them. So you can imagine my disappointment when the Anniversary versions of Halo were exactly the same game. A real wasted opportunity and it makes me even more bitter about Halo, on top of the fact that Microsoft are PC-hating jerks and don't want anybody to play it on PC. A simple addition like new weapons/equipment/enemies can turn a terrible remaster into a good remake. Therein lies my unreasonable hate for Halo (and the recent game on XBONE).
On the plus side, there's Pokemon ORAS. Pokemon Ruby on the GBA was the first Pokemon games and one of the earliest games (I got into games a bit late) I ever cared about and completed. I was very wary about Pokemon ORAS, especially since the newest games were released the previous year. I was in the mindset that Pokemon is Nintendo's equivalent of yearly COD/EA sports games and I even quit Pokemon, giving up all hope that it would ever be good again. But actually playing the game, it's almost completely different from the original and even from the game released just a year before. I remember hearing someone who doesn't play Nintendo games or own any of their current systems saying that ORAS is the best remake of a game ever, due to the sheer addition of new content and mechanics. I can attest to that. I spent my first several hours messing about with the new PokeNav mechanic in the first few areas. It gives me hope for remakes and I hope other remakes live up to the standard of what I though was Nintendo's cheap cash cow. Boy was I wrong.
I do think this topic of remakes/remasters needs to be discussed properly. I feel quite strongly about this topic, do remakes properly or don't friggin bother. I refuse to buy the same game again, just because there is no way they can just release the old game on newer systems. Change it enough to make it a significantly different experience to the original and I'll eat it up.