This title is technically the first in the series in chronological order. Clear Sky takes place before the events of Shaod of Chernobyl and is a solid title in ther series even if it is the buggiest and the worst of the 4. It easily has the highest difficulty curve due to its bugs but its still worth the play and still a great entry int he series. Highly Recommend it for anyone who is a fan of post apocolyptic style games.