If you were a kid during the '90's, it's very likely you had the real life version of this: those little egg-shaped devices that you took to school and got confiscated at least once or twice.
This is a PC-adaption of them, and while it most likely requires a Virtual PC (I am running it on Windows 98) to work, I find it to be a LOT more addicting than I remembered it being. You will need to insert the CD in order to hatch a new Tamagotchi, but otherwise no disc is required to simply take care of it.
It puts itself on a little window and while the window is active, you can hear music and your little blob making sounds as it does things. When inactive, the sound effects stop. The game is in full color, including your Tamagotchi. (Babies start solid black and white, though.) Whenever it needs something, the title bar and start menu icon will flash to get your attention. (Sometimes it does this when nothing is wrong, and you should scold it for that.) There's a care center where you can put your little blob when you're not on the computer, and if you attempt to shut down the game, it'll prompt you to send your blob there.
Just like the real device, the program is meant to be left running while you do other things, occasionally stopping to check on the Tamagotchi. If you're looking for a full game experience, this isn't for you. If you're looking to relive your childhood without tracking down one of those ancient Tamagotchi devices, (and then killing it by accidentally leaving it in your pocket and getting it drowned in the washing machine) this is definitely what you need.