I was really looking forward to this as I've been a fan of the resident evil series for years and always enjoyed the house of the dead style games at my local arcade.
However I must say I was a bit dissappointed, while it is an enjoyable game for the first couple of hours it soon gets annoying and frustrating when you have to shoot zombies in the "sweet-spot" on their foreheads to make any real progress with your end of level rank. What makes this worse is when you have a group of 5+ zombies lumbering towards you, while another decides to hide behind and projectile vomit at you. Boss encounters are also repetitive and long-winded.
Enough with the negatives though, UC offers the back stories of past RE games, albeit missing some games altogether, and so allows people who catch up with events. It also includes an exclusive episode featuring Chris and Jill bringing down Umbrella in Siberia. There are also a wide range of guns to unlock and upgrade although most are pointless and you'll more than likely just find yourself using machine guns and the good old zombie blasting shotguns.
Overall RE:UC is a game aimed at resident evil fans as non followers of the series will most likely be left clueless to the story and characters, and although I only gave it a 3/5 its a high 3.