A game of face palming and fist pumping
Spelunky is awesome... and terrible, but mostly awesome. Its a 2d platformer where timing your jumps may be the easiest thing you'll do. Imagine your Indiana Jones delving through caves, you want to take your time and use something like a rock to set off that arrow trap below you rather then your 'is not a pin-cushion' side. Rumor has it though that after say 2 minutes 30 seconds you'll feel the chill of a GHOooOOoooOOST (ok not that spooky I know but that guy 1 shots!).
However we all can't be Indiana Jones so to make up for his dope skills when it comes to dungeoneering the developers make each run through the game be different, sorta. It makes levels based off a randomly generated system that follows certain rules (mines always first 4 levels, then jungle, etc). So you know what lies in store, but you don't have an exact path to hone and speed through like you could with Mario Bros or Metroid Prime. Each time the turns and straights change and every drop you have to peek down for spikes could await you like that one time you thought it was OK and it wasn't and F$%# SPIKES...
Same Same but Different
So its another indie platformer but with always different levels, big whoop. Yeah its a game that has a speed record of under 3 minutes to beat and took me 50 hours played to finally take down Olmec in a 30 minute run. This game also has a hidden 2nd boss that you could reach and stomp in as quick as 9 minutes or if you were crazy take over an hour to carry an eggplant across the entire level to throw at is face... why? Because you can.
Its a game that makes you laugh at yourself and all the dumb stuff that you can do when you play a game that is built to not provide a linear scripted story of saving the universe or stopping a nuclear bomb... its a game about...
-Leaping across a gap to be greeted by a skeleton who punches you back into the pit below to land on a spike
-Throwing a rock the opposite way your facing and hitting yourself in the face knocking you into the hungry maw of a snake
-Getting a face full of blue frog that makes you stagger backwards into the pit of tiki-traps
-Accidentally throwing a rock into the shopkeepers store and hitting him, making that dude go
CRAZY
-Tossing a sticky bomb at an Alien Lord only to have his force field toggle on at the wrong time to have the bomb bounce back onto your FACE!
-Throwing Damsels (your most common source of +1 health) at bats flying to nibble your face off
-Tossing a bomb up at a large spiders nest and grinning with glee as the fuse shortens and death comes for it
-Looking down and seeing a caveman and a ledge and the rock in your hand that could bounce perfectly to take out the caveman
-Making it to Olmec's Lair and have NO IDEA WHAT TO DO
-Beating Olmec and wondering what other gems are left, cause there are a TON of things left to do...
It's a game that is about creating a story that is a memory of when you did something silly, or the game reacted in a way you didn't expect, or your first time overcoming some great challenge. Spelunky is a fun game you can pick up and play for 10 minutes at a time or find that you've slipped a few hours while trying to get to the city of gold.
Oh, and if you have a friend who wants to play locally you can do co-op but don't tell him friendly fire is always on and then he can be your "Spike-Inspector"