The Binding of Isaac is one of those few games I own in my library that despite its unforgiving difficulty and no saves, always keeps me coming back for more.
One of the reasons for this is its gameplay. The gameplay is top down shooter brilliance. While there will be times that the game will pull a ♥♥♥♥ move on you, (it can be quite luck based at times) you won't be blaming your death on a bug of any description. Unless you're a sore loser, but that's your fault, not the game's.
While the atmosphere may gross some very few sensitive souls amongst you, it has a reason for being that way and just enhances the (probably short) experiences throughout the game. If you've played Super Meat Boy, you'll feel right at home though, Edmund McMillen's the mastermind behind these two greats, and if you like his work, I also strongly recommend picking up the Basement Collection. Yes, I just recommended a game in another game's recommendation. (Recommendception!)
The real reason why I love this game so damn much though, is its stellar replay value. Every single time you start a new game, (and you'll probably start many) everything will be randomized. Enemies, boss fights, of which many are very challenging, items and powerups (good luck getting them all eventually) and rooms (some there to just screw you up with a deadly enemy mix, others with some goodies in) are all always different. Even if you beat the game fully once, there will be more things to do every single time.
Be warned though, that the DLC raises difficulty quite a bit. If you feel like you need to be eased into the game first slowly, you should play the vanilla first, and then activate the DLC. Besides that, the DLc adds tons of content and new fights and is most definitely recommended.
For its amazing gameplay that keeps you coming back after getting roflstomped, great replay value, and dirt cheap price, I can't give it anything other than a must play score, 9/10.