In my opinion, overrated. Yes it might regulate your temperature but only a tiny bit and certainly not enough to justify the cost. Also these garments often have complicated washing instructions.
A jacket can be good but only in certain situations and it has to be light and breathable. Through trial and error I've found that a waterproof jacket is a good choice when it's raining and under 10°C (proud of finding the ° on my mobile text!). Any warmer than 10°C and you'll be wet on the skin from sweat. I spent ages researching (not testing) a good jacket and found the OMM Kamleika Race Smock II with great reviews. Check out my review of it here.
Waterproof trousers are only required for slow running in very cold environments, rarely used. Compulsory kit for some races.
There are lots of choices! Have a range but notes that mittens are much warmer especially when you don't use the thumb and make a good fist.