3rd vs 4th edition

[fanghawk]

Just getting back into things after a layoff of a few years I had planned to use 4th ed. rules as I understood them to be generally a clean up and clarification of 3rd. Then I noticed hills were no longer limiting terrain...which I had to re-read several times and refer back to 3rd ed. a couple times just to make sure I was seeing that correctly.  Noticed the 2d6 Assault Table too...and recognized some codified Q&A from over the years...but thought generally everything else looked pretty much the same.  

What are the other changes impacting play in 4th ed.?  What do you consider to be the primary shortcomings?  While I'm generally replying to Pete's statement, I'd be curious to see what other's opinions are too.