One of the main things that made it harder to disassemble and also to repair is because the S5 is an IP67 (Dust and Water resistant) handset, this is specially complicated when putting the device back together which if not done correctly will make the device loose its dust and water resisting capabilities. The teardown also revealed a new battery shape similar to Apple’s iPhone size as shown in the image bellow (the new battery is the one located at the right)
The “L” shaped battery allows Samsung to make a much thinner battery. You can take a look at the video where ferra.ru takes a look inside the S5 and how to disassemble it.
Here is an album featuring images of the step-by-step disassembling of the Galaxy S5, for more images head over here