The Reapers are technologically superior to the organic species of the galaxy--but the degree of that superiority is a matter of debate in the intelligence community.
The Reapers' thrusters and FTL drives appear to propel them at more than twice the speed of Citadel ships. Estimates of their location in dark space suggest they can travel nearly 30 light-years in a 24-hour period.
Reaper power sources seem to violate known physical laws. Reapers usually destroy fuel infrastructure rather than attempting to capture it intact, indicating that Reapers do not require organic species' energy supplies. Consequently, the Reapers attack without regard to maintaining supply lines behind them, except to move husks from one planet to another. Unlike Citadel ships, Reapers do not appear to discharge static buildup from their drive cores, although they sometimes appear wreathed in static discharge when they land on planets.
The main gun on a Reaper capital ship dwarfs that of the Alliance's Everest-class dreadnoughts. No dreadnought has yet survived a direct hit from the weapon. Estimates put its destructive power anywhere from 132 to 454 kilotons of TNT. Even if the target is hardened, as in the case of a surface-based missile silo, the gun can instead bury the target beneath molten metal. Precise targeting computers and correctors also give Reaper weapons a longer effective range than organics' dreadnoughts or cruisers.
The kinetic barriers on a Reaper capital ship can shrug off the firepower of a small fleet. Weapons specifically designed to overcome shields, such as the Javelin, GARDIAN lasers, or the Thanix series, can bypass the barrier to some degree. The difficulty is getting close enough to use them--the surface mounted weaponry on Reaper ships, similar in principle to GARDIAN, presents an effective defense against organic species' fighters.