Dino Run can sort of be described as Sonic the Hedgehog meets Hudson's Adventure Island, only with the threat of total obliteration constantly nipping at your heels.
Apparently, the comet strike that wiped out the dinosaurs on Earth has just happened, and you are being pursued by the leading edge of the comet's impact wave. The goal is simply to race through each level before this Wall Of Doom catches up to and engulfs you, but you'll get bonuses for stopping to pick up dino eggs and bones that you find along the way. You'll also be alternately helped and impeded by other stampeding dinosaurs, meteorites, and crumbling terrain.
The game's graphics look like a cross between the Atari 2600 and an early '90s PC game, but the animation is all very fluid and there are some impressive effects like giant meteors slamming into the ground suddenly in front of you (and the Wall Of Doom itself, which is the first legitimately panic-inducing game enemy I've seen in years). I'm not sure how much of this exactly is intent and how much is simply working within artistic limitations, but it all ends up working out pretty well and lends the game a pleasant retro flavor without sacrificing gameplay or smooth movement.
The game has a lot of replayability; aside from a multi-player mode (the game is Flash-based and played on the Web), solo players can save their dino's statistics and achievements after each run. There's a bunch of trophies to be gained by accomplishing various in-game tasks, and DNA is earned in each game session which can be used to improve the speed, acceleration, jumping abilitiy and strength of the dino (eventually rendering him fit to take on the harder difficulty levels). You also change colors as you continually pass through higher difficulty levels.
Neat idea, fun game, appealing design; this is really simple free gaming at its finest.
* Play online