Alt-Tab is controlled by your Window Manager. Gnome uses either metacity or compiz if effects are turned on. They each behave slightly differently with Alt-Tab. I don't have any delay with either WM, Alt-Tab is quite fast on my system. If your using Compiz, you try turning down effects in
ccsm or try switching to Metacity. Alt-Shift-Tab also works with both WMs. I'm not completely thrilled with Metacity's behavior. When going backwards, it initially skips minimized Windows. Luckily, I rarely find a need to minimize, but it's annoying when I do. Based on your third point, it sounds like the Alt-Tab behavior of Compiz which is just like how Windows 7 ruins Alt-Tab if I hold on one Window for too long. That behavior can be configured with
ccsm under Window Management -> Static Application Switcher -> Appearence -> Selected Window Highlight. Try turning Opacity to 100% and/or changing Hilight Mode. Your second issue might be a problem with Key Bindings. Key Binding for Compiz are under Window Management -> Static Application Switcher -> Bindings.