Of course that’s not its full gamut.
I find all of these quite interesting as they represent additions and alterations that the games’ fans clearly desired. There’s quite a few of them too, so here are just a few that caught my eye:
Rockman 3 Endless
Something of a backport, this hack brings Mega Man 9′s Endless Attack mode to Mega Man 3. It’s a standalone patch, not just a small modifier, and it’s a good example of a feature/mechanic of a sequel that the fans wanted to bring back to an earlier incarnation of the series.
Mortal Kombat II Unlimited
It took ages of EGM posting certain spoofed rumours to convince developers of fighting games that implementing some playable hidden characters in their titles was a good idea. Eventually this became quite common, but not before Mortal Kombat II was released. To make things right, this hack not only allows the player to take control of the secret characters, but also to play as the bosses.
Chrono Trigger Coliseum
New worlds, quests, enemies, spells, etc., are always longed for with beloved RPGs, but realizing a fan-fiction piece in-game is quite a lofty task. Instead, this hack concentrates on providing a varied gameplay experience by creating an arena where the player (and optionally his party) can compete against numerous enemies for prizes.
Like I mentioned above, these are just scratching the surface, so what are some of your favourite ROM hacks?