I'm changing from assassination which is dual daggers to combat with dual axes.
But when I changed weapons, my crit chance dropped from around 43% to around 28%. I do know that weapons give certain bonuses, but I can't find anywhere which are theses bonuses. In the end, that difference in 15% crit chance is huge. What are these bonuses and where can I read about it?
You just don't have axes skill maxed. Each weapon skill level gives you 0,04% crit IIRC. So go hit some mobs till you get 400 one-handed axes skill.
Plus difference in talents regarding weapons and overall stat bonuses.