2005 is much like 2003, so if you didn't like 2003 you may not like 2005. There is plenty to gain from dropping vc6 tho, as vc6 was probably the worse vc version to date in terms of the absolute lack of standards compliance and such. Depending on what you're doing that might not matter to you so much.
Here's a sort of 'whats new' link if your interested.
http://msdn2.microsoft.com/en-us/lib...d5635e797.aspx