I understand this post is old but if anybody is still searching and has not found a solution to the intellisense issue even after re-installing, applying the cumulative updates, or other methods, then I hope I may be of assistance.
I have Applied SQL 2008 R2 Service Pack 1 which you can download here
http://www.microsoft.com/download/en/details.aspx?id=26727
32 Bit:
SQLServer2008R2SP1-KB2528583-x86-ENU.exe
64 Bit:
SQLServer2008R2SP1-KB2528583-x64-ENU.exe
I have applied this SP1 and now my intellisense works again.