Don't take the Glacier Express, not worthy except for Winter time.
Take a one day tour by bus to Luzern and Titlis. This is very good value (about $150).
You need two day to be in Interlaken. From there to take the local mountain trains and cable trans to different points to see Alps (Some places are Very expensive), Murren, Grindelwald are two good places.
Zermatt is a good place to visit also.

I spent 5 days with a 4 day flexible Swiss Pass going eveywhere from early morning to evening. My base is in Zurich. I was in Interlaken 2 times. The weather was not so good when I was there and mountain's weather changes instantaneously.

I will be there again next month but not for pleasure for sure this time.

Good luck