At speed, riding in the rain is pretty hairy.
On a recent ride we were caught in a bad downpour. Sure, we got wet, but having good kit does make a difference. Unfortunately for me my shoes are not the best and stopping at lights etc brought on the uncomfortable feeling of wet feet.
However, a steady cadence with a few hills warms you up. The only daunting prospect is descending in the rain. Obviously the roads are wet, grip is compromised and wet wheels = reduced braking efficiency.
If you descend in the wet as quickly as in the dry you are asking for trouble. I find steep descents the most daunting, especially those with twists and turns.
Go careful on the brakes, keep them covered at all times and descend with real care.
On the flat there is no real difference to dry rides save for the reduced vision, spray and of course loss of traction and braking efficiency.
In short. Don't be afraid of the rain, ride confidently but be a lot more careful and hold off with the Strava segment chasing. Save those for dry rides.