Although the Evangelions look like giant mecha at first glance, they are actually living, organic beings heavily outfitted in armor, which is not only there to protect them, but to also restrain their power.
An Evangelion can only be piloted by a 14 year old (the reason for the age restriction is unknown) whose mother's soul is hosted in the Evangelion. Through this, the pilot and the EVA can form a psychic link, allowing the EVA to be controlled by the pilot.
Super Robot Wars
In the Super Robot Wars series, Evangelions are depicted as slow machines. As in Neon Genesis Evangelion, EVAs must be attached to a power source; this can either be a battleship or, in Neon Genesis Evangelion-based missions, special buildings. They are very expensive if shot down, with repairs costs exceeding 30,000. (A vast majority of units have a repair cost in the thousands.)
The Evangelions' most powerful weapon is their AT Field barrier, which outright nullifies the attacks of most regular enemies.