I'm in Dhaka but never traveled by metro Rail Yet :-)
If you need to visit Uttara to Agargaon or anything in between like Mirpur, do give it a try, you would love it.
BTW, I also never traveled to any places in Dhaka. Sometimes I wondered why places in Dhaka didn't attract me!
Maybe you didn't have that reason to travel. Once you do then it won't matter if Dhaka attracts you or not.