Accurate - sans stock barrel
A pain to field strip
All things said, the US-5 is a great marker for what you pay. You aren't going to be blazing past everyone, but you will do well enough. It fires fairly rapidly, however, you will want to take spare batteries because the ROF diminishes quickly when the battery starts to die and you will need an electronic hopper to keep up with the AEC.
The barrel is something you definately want to change-out right away. I went with a barrel kit that accomodates a wide variety of paintballs. I have actually ran 2000+ balls through it and never had a chop (and I use relativley cheap balls).
I also added an expansion chamber to help conserve gas and the combat stock helps aiming (and looks pretty sweet).
You probably will catch quite a bit of flak from Tippmann owners, but you can quickly teach them to keep their mouths shut...I have nothing against Tippmann, its a great company with amazing products, but the US-5 works just fine for what I use it for.
I would recommend this for the beginning to fairly serious player. If you are going to be tearing up the fields every weekend, I would say go for the A-5 or a more high-end marker, but if you go out once or twice a month like me, the US-5 is the "perfect" marker