Everything will be different, it's just the age rating, for example
http://www.bing.com/images/search?q=...9871C9&first=0
Top right hand corner is the 18 pegi logo on ME3, replaced that by
http://www.bing.com/images/search?q=...03ACDB&first=0
Thats the only difference between UK and euro PAL releases, other than in the UK anyone could buy an 18 pegi rated ME3 as it's guidance, you'd have to show ID to purchase the 15 BBFC rated version as that is law. In Germany they tend to have the pegi logo shifted on copies and a USK logo either as a sticker over the pegi logo or printed on the box next to the PEGI logo.
No real difference but I'd rather get BBFC logos where available as that is UK Stock and I believe less in comparrison to the whole stock allocation for the EU so might one day be worth more to other collectors. I'd pay a lot of money for a Metal Gear Solid 4 UK PAL Play.com exclusive collector Edition, where I'm trying to sell my EU PEGI rated version.
(I never used to be sooooo OCD)