The IT infrastructure is horrible, to the point where it is amazing the Inspector General has not intervened. They implemented a new timecard system, Paycheck 8, which cannot accurately track employee sick time, leave, or vacation. There are IT systems which use components 10 years past end of life. If you can tolerate the significant impairment not having reliable IT systems will have on your ability to work efficiently, it is a great agency.
Do not ever accept a term (temporary appointment) with the FCC. While such appointments are frequently converted to full time positions, HR will not offer any of the traditional flexibilities such as leave credits, step exceptions, signing bonuses, tuition reimbursement, salary matching, etc. to anyone serving on a term position. They will have you over a barrel and will not negotiate. If you accept a term position, apply to other agencies for a more lucrative permanent offer before your term expires. Do not expect a competitive offer, expect to be lowballed.