Yep I am quite disappointed about that one too but it is easily fixed - there is an app that when you click on it provides the slider for the screen brightness. I like ICS too seems to waste a bit less battery than Gingerbread and also we have support for the new protocol (mobile network and APN settings. I think its called IPv6 which seems to get my internet going a bit faster.
Anyway I think just like with every new software (especially microsoft windows cough cough) there will be quirks that are not very appealing. The windows comment is coz last time I could not find where control panel is when I was looking at windows 8 or what ever the new stupid thing is. You can already tell how exited I am about it LOL