The binding of Issac is a indie game. It's like the Legend of zelda inside the dungeons from NES and Snes as per looks. As far as feel it's kind of unique: http://www.youtube.com/watch?v=6Irm_scgytY .
It's a petty fun game with a fairly high level of replayability. It would be nice to see a free alternative. Though I'd see a few changes. Being built in flash came with a number of obvious limits. The creator implemented classes with select itemization and stats. Cain is a "thief". He starts with a key and a lucky foot. The foot gives him better odds at mini games an makes sure pills give only beneficial stats. Eve the "druid" starts with a pet that activates while take a hit and a stat boosting transformation when she gets to half a heart. Ect.
The stats are simple. Movement speed, attack speed, Attack power, Attack range.
Instead of implementing classes I'd set the starting stat weights to a certain level and have them manipulatable. I'd have a choice of certain starting items (once they are unlocked) Limit to one or two. I'd add multiplayer mode and a death match mode. I'd choose a more neutral lore base than the bible.