Fender MIM instruments are generally very good to excellent. The Classic/Roadworn Series are regarded by many to be equal to or superior even to American Standard/Specials. One cool thing about the MIMs is their compatibility with the majority of MIA necks, bodies, and parts. The wood quality is often a step below the MIA, but the parts/electronics are generally on par. In the end, a MIM is less expensively produced than an MIA, but that doesn't mean that you end up with a less-functional instrument. The Ensenada plant is about 35 years old and only about 40 miles or so from the one in Corona, so they know what they are doing down there.
The only MIM models I generally don't like are the Standard/Player Series Telecasters. For some reason, I find myself preferring the MIA versions. Sometimes I'll find a MII CV/VM Squier that I absolutely love (I have a VM Surf 60s Strat that is a true keeper).