If you liked Resident Evil 4, pick up this game.
The graphics in Resident Evil 5 are amazing. Beautiful cutscenes and gorgeous (for zombies, anyway) models. The sound is also excellent. However, the game has lost some of the horror feel of the previous installments, due mainly to the lack of missions set at night or in dark hallways. The voice acting is a cut above average, and the storyline, while inherently implausible, is engaging.
The introduction of the new mechanic of having a partner is well implemented and the AI is capable. Only once or twice did I feel that my computer-driven partner was holding me back. The new inventory system adds an extra rush of adrenaline to the game, as now you can't pause to access your inventory, and you can only carry nine items at a time (although you can keep plenty in storage at the shop that is accessible at the end of every sub-chapter or whenever you die.) There are plenty of different weapons to upgrade, all of which have their own strengths and weaknesses. Finally, with four difficulties and plenty of other challenges to accomplish, you'll want to keep playing long after you finish the story for the first time.
All in all, Resident Evil 5 is a great game.