I've a 640 on WP10 its vibration is much weaker than any other phone we have. The Lumia 520 was poor this is worse. Anyone else the same? Maybe mines faulty.
I have a lumia 735, and I also have weak vibration. There are many missed calls and unanswered messages because of that. Its just how it is, you should check your phone every few minutes so you don't miss anything