Its not uncommon, gutters (especially long runs) often overflow with heaviest rains, as long as most of the time they prevent water running down walls then they are doing their job.
Debris collects in them (especially at joins where moss holds a mass together), it might just need a quick clean-out. Some window cleaners will do this cheaply.
I laugh where the downpipe is just round a corner, there is no way the water is going to turn ninety degrees without sloshing out when its at full flow. I always picture the Winter Olympic toboggan fails.