Yeah, spring is definitely coming (for how long is the good question :p). Paris is very nice when the weather decides to be pleasant (this means not too wet, not too hot), which means not too many days in a year (yeah, it is easy to complain ;) ).

More seriously, the city is really nice with beautiful weather. People are smiling more, paying more attention to others, etc... But I guess this may be true in any big city...