In melee your character "landed" when their shins/knees touched the ground. In brawl there's a hovering specific point below your character which determines when they land, it's usually much closer to the feet. The affects things like Ganon not being able to make it to the lower platform on DL in one full hop, CF not being able to second jump waveland across YS plats, and other minor things like some characters landing earlier from aerials (it's more difficult to double SHfair with marth for instance.)
To be continued...
Shield timing is different in that there is still only brawl shields, but that now instead of activating on the click of the shoulder buttons, it activates on first depression. This includes air dodges (rather than click you must just press lightly.) This affects WD timing, since you no longer have to press all the way down to get a WD and can potentially lead to botched WDs. It also affects specifically shield WDs, I believe, since the timing is usually tighter, and also results in you not being able to shield WD with one button like you could in melee.
Like I said, it's basically what I hoped brawl to be in its initial release. There are some small changes, but that's to be expected with any new game; not the overwhelming mass changes of brawl originally. I can handle the small differences.