My current campaign features quite a few "PC like" NPC's. The way I handle them mechanically is to use the monster builder and start with a "monster" base template of same race. I will add and substitute powers from PC classes to the NPC in order to give them a feel similar to the class I'm trying to emulate. Some daily type powers can become rechargeable for elite/ tougher NPC's.
There is nothing quite like the look of shock on a player's face when some of their favorite staple powers are used against them. The groans of doom heard heard round the table when an evil enemy ranger uses -DISRUPTIVE STRIKE!! was worth every moment of monster builder design time.
Yeah that's the reaction I'm hoping for

I'm playing around with the monster builder, but I'm pretty noob at it and it seems to take ages to craft a single NPC. I'm not sure I understand how the monster builder works. Adjusting the ability scores don't seem to have much effect on the monster defenses and powers?
Are monsters essentially PCs without feats, limited racial & class features, less powers and lower defenses?