Fenders are great, make sure the front one has a flap that ends around 4" from the ground and you will keep a lot of road grit, oil and water from coming up onto you (and your bike) from the road surface.

Lights are a wonderful safety feature, a Dinotte taillight is a beautiful thing if you value your life much.

Disc brakes work as well in the wet stuff as they do in dry weather, rim brakes require that you "adjust" the way you ride in the rain, they will smear and scratch your rims.

If it's dark and wet you will not be able to tell how deep the puddle is, could be a half an inch or two feet deep, it will look the same.

Your feet will get wet (much less so with fenders), because rain water will go into your shoes by running down your legs.

Heavy rain sucks to ride in, all other types of rain are OK unless you add other weather obsticals (like wind or cold) to the mix.

You should immediately dry and re-lube your drivetrain after a wet ride, don't let it sit wet.