Amherst is known for its teachers and this has not diminished. Your experience will be determined more by your teachers than the facilities. The facilities are getting a major upgrade (reflecting Amherst’s commitment to the sciences) and it should be ready for your senior year.
In case you haven’t read this post (http://talk.collegeconfidential.com/amherst-college/904517-science-at-amherst.html), it talks about science at Amherst and students speak highly of the biology department.
Congratulations on your acceptance(s) and it sounds l like you have made the choice to attend Amherst. Don’t put too much weight into ratings - relative positions in the top LACs are arbitrary. Once you’ve made the choice, celebrate and don’t look back.