Difference between Warning and Critical Warning

As far as i understood this, critical means that you should check this warning as it could mean that your design might fail or even wont behave as you expect.

critical warnings are timining violations for example. your design might work at 25 degree celsius but it might fail on other temperatures.

some warnings are only informational if you know where they come from and why they are generated.

for example if you assign a signal array with a different width to another signal array. in verilog a warning is generated if you have "a <= a + 1" where a is a register of n bits and you will get a warning that the "1" will be truncated to the width "a" has. so you can ignore that warning or correct your sorce a bit

but a warning itself is not an info message and you should look at the source of that message.