chautemoc: Lemme know how it is, curious about that one. Gonna give it a go for my next playthruogh.
So far, it is pretty much what it says on the tin. The gameplay mechanics have been altered mostly in the name of realism, or simply making the game harder, although it feels like it could be taken further. Can't comment on all of it yet, but here goes:
The SPECIAL system means quite a bit more than it did. Strength has a far greater impact of your carrying capacity, agility has a much greater impact on action points, and endurance greatly impacts your starting HPs. For example, your base carrying capacity is 50, and each point in strength adds 20.
Weapons are stronger, and you will probably tear through some of the earlier creatures, but to counter that, most humans have better armour (or the armour has been adjusted to be better) and weapons themselves, and will (as I understand, not got very far with it myself) be much harder the further you get in the game.
You can take damage in VATS, and your weapons degrade at twice the regular speed when used in VATS.
You can also adjust the speed at which time passes. The default for the mod is 4, i.e. for every hour you play, four hours pass in game. You can also adjust how much xp you get from quests, kills etc. Default for the mod is 1/4 of normal. Both can be adjusted on the fly in game.
Basically, from what I have played of it, it feels like what it is, a bunch of difficulty tweaks. Will have to play more to see how it impacts the game in the long term.