During Overcast it still looks dull and there really is no light effect at all. But that is like it is in real life, but it doesn't look amazingly good :/
When you play in rain at night it looks good - You have mirror effect on the ball and on the player boots and the player kits get wet - But for me it doesn't look like it has been improved over FIFA 11
But in the Day/Dry and Night/Dry/Rain time is where it really shines

The lighting effects is really good and the players looks more detailed.
Playing at Old Trafford during Night (Doesn't matter if it is dry or rainy) is really amazing. The grass looks really short and the field is lit up great and you really feel like it is like playing a real Champions League match (My first match was Man United vs. Aalborg BK during night).
But I had a great game against my brother where he was United and I was Fulham and we played it during Night/Rainy and it felt like a real Premier League match with intense tacklings and really great passing play.
So overall it has been improved from last year
BY THE WAY!
The ball physics felt weird last year playing in rain (The ball made this weird thing where it stopped - Like there was a pool of water) - It feels way more realistic this year