The greatest Minesweeper game I've ever played. Not only is it the current record on my computer, but I also uncovered a 6 and a 7 in it.
In my opinion Minesweeper is the most awesome electronic puzzle game ever made, paws down. Like Solitaire, it's best played when you're waiting for your computer to finish doing something like download a huge file or upload something to DeviantART. Like this pic for example. Sadly many people have seen Minesweeper and not bothered because they didn't figure out how it works, or they know how to play it but just can't figure out how to cruise through it the way they've seen people like THIS guy do it: [link]
The objective is straightforward. You're on a minefield and there are 99 mines (in the hard level anyway). Now IRL, you would just call some military person and have them rescue you in a helicopter and simply surround the whole area with tape and a warning saying in several languages that this is a minefield. But this isn't real life is it. Instead you have to do something much dumber and more pointless--dig through the ground in EVERY spot in the field that DOESN'T conceal a mine. In other words you have to reveal each button that isn't a mine by left-clicking on it. From here it actually starts to resemble RL again; if you left-click on a mine, it blows up in your face. Game Over. No, you don't have "Shields". This isn't a Dark Forces game. Right-clicking will put a red flag on that square to indicate that you've decided you think a mine is there. But flagging all the mines won't win the game; otherwise you could just flag the whole field (like you'd do in real life) and win automatically.
There's a total of 10 different things that left-clicking a button and revealing the contents of that space can yield. 9 of those are visible in this game. It could be...

...a mine! You win a Darwin Award! Congratulations! You're supposed to RIGHT-click on mines instead. If you move on to a square that you think is probably a mine, right-click to place a flag on that button without actually revealing it. If you die later you'll see where all the mines are and which flags you used correctly.
...a number. This means that you clicked on a space that has a mine right next to it. It could be from an 1 to an 8 depending on how many mines are surrounding that square. 7s are rare, but I think you're more likely to see a 7 than to go a whole game without getting any 5s. 8s are extremely rare--if you want to see one just to know what it looks like, pick the "custom" difficulty setting and put in 435 mines. This'll probably work because the first button you left-click is always safe.
...NOTHING? A square that has no mines surrounding it (I call them 0s) has an effect of automatically opening up every square surrounding it, and if any of those squares are also 0s, then even more open up, creating a rather interesting "expanding" effect. If you get a 0 on your first click then you're off to a promising start.

Tricks I learned.
1. 3 bordering a 0 region: Imagine a 3x3 grid. The top three squares are 0s, and the second row reads 2 3 2. All three on the bottom row are mines.
2. 1 2 1: Imagine a 3x2 grid, and the top row reads 1 2 1. The lower-left and lower-right squares (adjacent to the 1s) are mines.
3. 1 2 2 1: The squares adjacent to the 2s are mines.
4. Wild guess (2 squares): sometimes you box in a pair of squares and know that one of them is a mine, but there's insufficient information to tell which one is a mine. Guess it right now to get it over with. Unfortunately this is where the 50-50-90 rule of Murphy's Law kicks in, which dictates that if you guess randomly in a situation where you've got a 50% of being right, you'll be wrong 9 times out of 10. Tough luck.
5. Wild guess (3 squares): Two situations here. If two of the three are mines, then you're even more screwed than in the above situation, with only a 33% chance of survival. But if only one is a mine, choose a square on the side, NOT the one in the middle. 2/3 chance that it'll be a number, and if it is a number it will tell you which of the remaining two squares is the mine.
6. This won't work in Windows Vista, which is yet another reason why you shouldn't use Vista. Type xyzzy then hold the Shift key as you press Enter. At this point if you mouse over a square containing a mine, the pixel in the upper-left corner of your computer screen will turn black. Use this to get out of aforementioned Murphy's Law situations.