In The Groove (PS2)
In The Groove was made by and for dance game fanatics. The core new feature is a large set of modifiers ("mods") which change the way the arrows move along the screen. In Marathon Mode you play a preset menu of songs in a preset order with a preset sequence of modifiers. There are still arrows to indicate steps, but rather than the arrows marching uniformly up the screen they swoop in, or they move in waves, or they spin as they approach targets which are also allowed to meander about the screen. The upshot is that you are really forced to get in the groove and step based on the beat more than the onscreen graphics.
The background is simplified compared to standard DDR - there are no annoying onscreen cartoon dancers or full music videos to distract from the steps and the music. The normal DDR difficulty scale goes up to 10; this one goes much higher by adding mods and hand steps - places where you have to drop to the floor and slap the pads with a knee or a hand to trigger three or even four spots at once. The game also adds bombs - moments when you need to not be on a specified pad to avoid losing health and points!
For working out, Fitness Mode lets you play a random selection of songs at a given step difficulty until a specified calorie total is achieved. Recently I've been using it to play 1000 calories' worth of 6-foot songs a few times a week. Note that In The Groove extends the scale in both directions - compared to a standard DDR game it has more super-easy step sequences to get started with as well as more super-hard ones to work up to.
All in all, In The Groove is a worthy addition to the DDR genre. Hard-core players should buy it immediately (or at least, as soon as they get tired with their current game). First-time players might find it too intimidating and be better advised to start with a more traditional game - I suggest DDR Max 2.