Clearly you have to get used to the new GUI which ships with Leopard. The most ‘in-your-face’ changes are limited to the Dock, Finder and the Menubar. Actually the Dock looks fine, except those indicator spots beneath the icons,.. those look awful. Fortunately you can easily customize them by replacing three files in your dock.app : /System/Library/CoreServices/Dock.app :: Source: Silvermac.com

If your sill not satisfied with the look and feel of your Dock, you can also replace the texture of the shelf, take a look at LeopardDocks.com
Then there is the tanslucent effect in the menubar, which offers a glance at the wallpaper. Some tricks to alter include :

• Install the OpaqueMenuBar ultitly from Eternal Storms Software
• The easy solution - if you can live without a stylish wallpaper - is :

    (A) to edit you wallpaper of choice an and a 21px high white strip at the top … read about it or
    (B) to choose a solid color as background, preferably the darkgray one :

Last but not least, some changes within Finder. I’m not really fond of the default Leopard icons, but I guess it’s a question of getting used to it. (besides once CandyBar 3 is launched, I’ll customize them anyways). The use of alternating colors (white and babyblue) if the List view is choosen is also a new one, perhaps we’ll be able to change it to plain white sooner or later….