The Angel is considered by most to be the pièce-de-résistance of paintball technology. It is fully electro-pneumatic, meaning that everything is electronically controlled. In a standard paintball gun, a mechanical sear holds the bold back until the trigger is pulled. Then the bold moves forward and strikes the valve which releases a burst of gas. Some of this gas is used to propel the ball out of the barrel, and the rest is used to push the bolt back against the sear, resetting it for the next shot.
However, in an Angel, everything is electronically controlled, from the amount of air released to the cycling of the action. This allows for almost no moving parts, and makes the entire gun extremely precise, accurate, and programmable for different modes of fire.
This comes at a high cost, though, as the average Angel costs around $1000 without upgrades. It also cannot take the relatively coarse nature of CO2, so must be run on HPA.
Since Angels are so expensive, the average player customizes his marker to reflect his personal style. Here is a good example.