Not too bad of an experience, but you will be treated like your getting on a plane before entering.
I understand that security in government offices is a good idea and that some peoples entire incomes and citizenship may ride on these employees decisions, but a full on TSA vibe walking in seems like a little much.
That said, the whole place is ran rather smoothly. Nothing like the DMV, most of the people are smiling and are actually helpful. Not a place you need to go very often, but unless your getting deported or something, it shouldn't be treated with the same dreaded "Do I really have to go deal with these people", like most intercity DMV offices.