Back before PopCap was bought by EA and the company saw the detriments that the very move brings, they made the most awesome "casual" games that somehow intrigued both casual and hardcore gamers alike. PopCap's major successes include Bejeweled, Peggle, and Plants Vs. Zombies, but through playing all of their games for the past twelve years, Insaniquarium is by far my personal favorite, and in my opinion, the most original, creative, and fun.
This game is part simulation, part "management", part tycoon, part action, and all sorts of...well, insanity. You are put in charge of an aquarium, where you can buy goldish, carnivorous fish, and many other types of creatures that you grow and make money off of. (First win of the game: goldfish poop money!) You use this money for upgrades (upgrade the food to make the fish grow faster and get hungry less often, buy carnivorous fish that poop diamonds but eat little goldfish, etc.). You have access to dozens of unlockable aquarium pets throughout the game that help you in various way, and you choose which three you'd like to bring to any level. Oh, but I haven't mentioned the aliens. That's right, folks, aliens are so jealous of your awesometacular aquarium that they'll attack, and throughout the campaign the aliens get fiercer (and sometimes come in multiples!). Aliens will eat your fish, but not if you kill them first with a laser gun that you can also upgrade...with the money your fish poop, of course.
Not only does this game have a great campaign that will keep you busy over the course of quite a few hours, but it also presents new challenges to the player along the way, in the forms of various alien types, different fish you have to figure out how to make profitable, etc. Not only that, but throughout playing you'll unlock sea shells that serve as currency for a "Pet Aquarium", where you can purchase fish (among other things) for a relaxing sim aquarium. These fish are essentially the same species from the game, but they come in a large variety of color combinations and sometimes even have special skills (some hilarious, some useful, etc.). What's even better? The selection of fish in the store is randomized and changed daily, meaning you'll come across some really awesome fish one day that you might not see for awhile again, so you can save your shells and get rarities or even just cool looking fish to add to you aquarium. You can collect quite a few, and you can even name them. You also have access to their "interests" screen, where you can learn more about your fish. Does Gill like to take walks in the park? How long have you owned little Floater? You can see all that and more.
Insaniquarium is a perfect example of PopCap at their finest. Sure, the game is "casual", but it offers you so many options and it has so much detail that many developers wouldn't have added in (like telling you your fish's interests, for example). If you are a fan of PopCap's earlier work, buy this. If you are a fan of simulation or tycoon games, buy this. If you are looking for a game with a sense of humor to pass a few hours, buy this. This is PopCap's best effort, and will forever be a classic.