I love how they flow together with part 2 happening about less than an hour of the ending of 1. Shit was intense too! I agree that part 3 wasn't really that good so I usually tell people to avoid or or watch it after 1,2, and 4 since those are fit the timeline and make the most sense. 3 can be watched as a side movie that doesn't have anything in common with the rest, or totally ignored all together.