I have recently acquired a Game Boy Pocket. It is one of the revised models, with a blue case and a power LED. The Pocket is a slimmed-down version of the original Game Boy. Its chief benefit is that its case is smaller and less bulky. It has a similar screen size but slightly smaller controls and speaker. It plays the exact same titles as the original Game Boy. It doesn't have a backlight, but one can be added today with mods.
The screen is the best feature of the Game Boy Pocket. It has better contrast than the original, a better monochrome gradient and virtually no ghosting with moving images. The original Game Boy screen, due to pixels with long transition times, would show ghosting in moving images. Some games have effects that require a monochrome screen, like the mountains at the beginning of the Cloud Castle stage in Castlevania 2 : Belmont's Revenge. On any color screen, the mountains will flicker more than on a monochrome screen.
When I play a game on the original Game Boy, I have asked how I ever put up with that awful screen when I was a child. I do not ask the same thing about the Pocket. Another plus to the Pocket is that it does not suffer the missing vertical lines issue of the original Game Boy screen (fixable, but still).
The sound has been criticized as not being as nice as the originals', and from the headphone jack there an annoying background noise that is audible when headphones are connected through the headphone jack. The original Game Boy just has hiss. Stereo panning support was a touted feature of the Game Boy when first released, but by the time the Game Boy Pocket was released in 1996, there were few music and sound effects in games that supported stereo sound. Most people used the built-in speaker, even when headphones could be used.
The controls on the Game Boys and Game Boy Advance feel like real D-pads, the controls on the Game Boy Advance SP feel more like microswitches. The controls on the Pocket are not so much smaller than the original to really feel like you have lost precision control.
Backlighting kits exist for the Game Boy Pocket, typically kits work for the original and the Pocket. The best ones are from nonfinite electronics and kitch-bent. Installing a backlight in the Pocket is a bit trickier than in an original Game Boy, here is a good video showing how it is done : http://www.youtube.com/watch?v=qUUEVWbLoS8 A Youtube channel now called 8-bit guy suggested spraying WD-40 into the crevice between the layers and the glass once you have pulled up a corner. He says this really helps remove the adhesive bond. Having irreparably damaged a Game Boy Pocket's screen after trying a mod without WD-40, using WD-40 may be a good idea.
The only real disadvantage to the Pocket is its anemic battery support. The original Game Boy uses four AA batteries, and the Game Boy Light, Color and Advance all use two AA batteries. The Pocket uses two AAA batteries. An AAA battery has about half the rated mAh as an AA battery. While this is OK for playing official cartridge games without a backlight, it is far from ideal for using multicarts like the EMS GB 64MB Smart Cart or the new Krizz Everdrive GB. A backlit GB requires more power than a non-backlit GB, even with modern LED backlighting. Multicarts require more power than standard carts
In my opinion, Alkaline batteries may be okay for a backlight, but they do not have sufficient power for a multicart. On the EMS card, the cart may work for a while with fresh, name-brand batteries, but after a short time they will not be able to power the card, which will lead into an endless reset loop. Alkaline batteries experience a far greater mAh drop over use than Lithiums.
Perhaps the EMS cards made after June, 2010 (as shown on the back of the card, mine is 0908) are better with this. More active screens will appear lighter than less active screens. NiMH batteries tend to support 500-800 mAh compared to the 1250-1000 mAh of the Energizer Ultimate Lithiums. 1000 mAh average is probably the maximum you will get out of name brands, but I hear they can provide a much more reliable current than an Alkaline. I would strongly recommend using the Sanyo Eneloops or other high end brand.
There are AC adapters for the Gameboy Pocket. The right adapter for the Pocket or the Color uses 3V, 300mA and has a positive tip. Radio Shack's Adaptaplug A should fit.
My EverDrive GB will work in my Game Boy Pocket with Sanyo Eneloop rechargeable AAAs. The screen contrast will lighten somewhat when it is loading or flashing a game, but it will complete the process. When the game is playing there will be no need to constantly monitor the contrast dial as I would with the EMS Flash Cart.