They're both extremely linear. There are larger areas that you'll run around in during firefights or to solve puzzles/platforming, but you're always on a one-way path to your objective. You're looking at ~10 hours each depending on the difficulty and how many treasures you find. As for which to play first, I'd definitely go in order. One of Uncharted's greatest strengths is its believable, likable characters, and while Uncharted 2 is very much a standalone experience in terms of main story, the character development from the first game to the next is some of the best in gaming in my humble opinion.