Highly addictive at first, but the thrills are short-lived.
The major twist is that every so often, an alien (or multiple aliens) will appear in your tank and try to eat your fish. You must kill the aliens and protect your fish. If all your fish die, its game over.
The game starts out really fun actually. There's something really addictive about raising and protecting your fish, and its exciting to unlock new helpers for your tank. The game also implements various twists in each tank as you progress through the tank, such as carnivores that drop lots of cash but need to eat baby guppies to survive or potions that you can drop in your tank which improve fully grown fish but instantly kill smaller ones. There's also a fair variety in the aliens that attack your tank.
The main adventure mode takes about 3 hours to finish. This is really the bulk of the game, so its kind of disappointing that it's so short. You can play it over to gain points to unlock 4 more bonus helpers, or try one of the 3 other modes: time trial, challenge or virtual tank.
TIme trial is pretty self-explanatory. Challenge mode forces you to complete a level with ever inflating prices on the items and enemies that continuously get more challenging. Both of these modes give you points that you can spend on bonus helpers or in the virtual tank. The virtual tank allows you to buy and feed fish for your tank, which you can set as a screen saver. Some people may find this interesting, as depending on which day of the year you play, there's different items in the shop. Overall though, threre's really not much to see here.
Insaniquarium Deluxe is a really fun game at first, but its over too soon, and there's little to keep your attention after beating the main game once. Retailing at 20 bucks, Insaniquarium just doesn't offer much bang for your buck and you'll likely end up feeling cheated.