Peggle Extreme is a variant of Peggle (Deluxe) from Popcap Games. It was offered with the Orange Box and it's not really a surprise: Popcap Games is also using Steam (mandatory when playing the Orange Box on PC) for broadcasting games made by them.
The story of Peggle Extreme is simple: you have to defend the Peggle Institute from invaders during 10 levels. Let me explain the gameplay. You have peggles on your screen. Peggles are these points or rectangles with different colors. Blue ones are the basic peggle, the orange ones are the ones you have to eliminate, the green ones are the speciality from your guide (in PE, it's only Bjorn the Unicorn and the fact that he can show the trajectory of your ball) and the rose one are point boosts and are chosen randomly when launching a new ball. The goal is to launch a ball and eliminate a maximum of peggles. I mean, with ten balls, you've had to eliminate every orange peggle, others being point bonuses. You have a bucket moving at the bottom and you can earn a free ball if the one currently launched falls into it.
You can also earn free balls by reaching a certain score with one ball during its play. The first step is 25.000 points. Also, you have the fevermeter. When reaching the X2, X3, etc., it increases the points tied to peggles: for example, a blue one that brings 10 points when touched is bringing 20 points when touched when your fevermeter indicates X2. And it's valid during all the level. There are also special bonuses like the long shot (touching two peegles far away from each other) or the lucky bounce (the ball touches the bucket, is bouncing and then falls into it. If it don't fall into it, the lucky bounce is missed). If your ball falls into the void without touching a peggle, you will have a coin with Free Ball or No Ball appearing. It's randomly, so, you can only pray that you'll have a second chance. That's only a view of the bonuses existing (you have extreme slide, orange attack, etc..). When finishing a level, the bucket disappeared and five special bonuses appear: 10.000 at the far left and far right, 50.000 for the two others and for the middle, it's 100.000 points. Note that if you clean your screen of all the peggles, you're unlocking Ultra Extreme Fever and all the five voids bring 100.000 points.
You have also special features for the duel mode: -25% of your points if the ball doesn't touch a peggle and falls directly in the void or in the bucket for example.
The backgrounds are customized to the Orange Box games with Peggle Masters appearing in it. Half-Life 2 Episode 2 is represented by a Vortigaunt attacking a Peggle Master, a Headcrab, a Hunter. Team Fortress is symbolized by an Heavy with a Peggle Master, a sentry build by an Engineer, a Pyro pursuing a Peggle Master and a BOOM! probably taken from a trailer. Portal is more interesting by the fact that you have portals that change the location of your ball. You have the lovely turret and the Weighed Companion Cube. Every game is featuring the voice of characters appearing in it. For HL2E2, it didn't really let a trace in my brain but for TF2, you have the voice from the Heavy, like the "You did well!". For Portal, it's our dear psycho Glados.
As you can suppose, graphics are simple, not really complicated and very cartoonish for the Peggle Masters. Backgrounds are more similar to the original graphics of the game than being cartooned. Soundtrack is also perfect.
The different modes are also challenging. Duel Mode is made for playing alone against the computer or for playing with a friend. Adventure Mode is the solo campaign. The Quick Mission is for playing unlocked levels and the Challenge Mode is for people liking Challenge. It's a sort of Bonus Map like in Portal: you have to beat the challenge for gaining the title of Peggle Master for the level: clean all the peggles, reach a certain high score: 300.000 for example, eliminate all the orange peggles (the classic gameplay). I can guarantee you that reaching a high score is easier than trying to clean your screen. Currently, I'm a Peggle Master in each level, the last title is the cleaning of the first level with the Vort.
Peggle Extreme isn't suffering from flaws, apart the shortness of the game, being a product designed for the Orange Box and the fact that you will not beat every level at your first try. Believe me, you'll find the BOOM! and the sentry levels very challenging. And wait to see the level from Portal and its three parts you can only access by taking portals.
Anyway, for me, this game is really enjoyable, if you don't try this, you don't know what you're missing. I mean, if you can afford the Orange Box or if you can buy on Steam. Peggle Extreme is probably one of the best casual games I've played and I'll admit it: seeing G-Man as the sun or Bjorn with a Headcrab is something that HL fans can't miss. Anyway, I'll recommend it. It's fun, very easy to understand and enjoyable.