The patch is not compatible with your saved games, so you'll have to start a new game once you apply it.
One good single-player change is that now money is worth something. Traders have some decent items (The Trader Cid has a Merc Suit and Stalker Suit for sale, which is cool). The bad news is that now armor degrades (after a while your %15 rad protection suit drops down to %4 rad protection), and people can't find a way to repair it. This is gamebreaking IMO, as it's unfair to expect me to keep finding new SEVA suits. And no, the Freedom base vendor dude does not repair armor in the patch, according to some Stalker forums.
A great game, but it could have been so much more. It feels buggy and unfinished. Disappointing...