Retro Achievements is a community effort. You can make achievements yourself or suggest them in the game's thread.
Learning how to make them isn't very tough, but can be tricky setting up or even impossible depending on the achievement and game.
If you have any questions, feel free to ask in the forums or chat.
There's leaderboard support as well. For example, I did some work on Super Metroid leaderboards
here, using the in-game timers. Ceres Escape, Any%, 100%. I've done the same for many other games such as SMK, GBA metroids, DKC2/3...
Hardcore mode is an option in the emulator's menu, which lets you earn double points from achievements you unlock at the cost of disabling savestates. There's a bunch of statistical features on the site to see as well.
A very small taste:
Badges with a gold outline were earned on Hardcore. There's been some debate on how the gold outline looks, but we haven't come up with a good replacement.
There's only one guy setting up the site and the emulator integration, so it's going pretty well.
Note: We want to avoid achievements that
require glitches, though exploits like spamming 1ups from goomba kills in SMB3 are welcome. Abusing glitches to get good leaderboard entries is accepted as well.