When Magneto was originally created back in the 60's (alongside the X-Men), they gave but a brief description of his powers; the ambiguous Master of Magnetism. This would give one a good deal of leeway when it comes to concern of actual application. Magneto's abilities are astounding enough that the Government and a few others built quite a good deal of defensive measure just for Erik Lennsher, a few being plastic-and-porcelain Sentinels, a plastic prison, magnetic disrupters, nonreactive metals, to name a few. If you question is really about the few limitations and extreme abilities of Magneto, then yes, he is rather Godlike in his abilities and output.
But he isn't alone.
Erik Lensherr is an Omega Class Mutant, which is a designation of categories that rate the powers, output, and abilities of a neo-homo sapiens superior. While an Alpha is generally considered first tier in scope, the Omega designation is for Mutants that could quite literally kill the population of the planet, or deal enough devastation to cause so, regardless of circumstances or special instances. Phoenix (Jean Grey) is one such mutant, who is considerably more powerful, as she could conceivably drain a star, and possibly disrupt enough to destroy the galaxy under circumstantial conditions, thanks to the M'kran Crystal. Professor Charles Xavier and Scott Summers (Cyclops) are Alpha Class, which while still incredibly power, do not have the ability to do so under normal circumstances. Yes, Professor X could start a nuclear war with his telepathy, but his power itself could not do so; Magneto can affect the magneticsphere, which would increase solar radiation and genetic mutation. It is also wondered that he could slightly affect Earth's rotation, orbit, and position. Such a feat probably would kill him, but it might be under the scope of his powers.
When many superheroes were created, their powers were more or less limited to the Age they inhabited at the time. Superman and Green Lantern (the original one) had powers that were significantly lesser than they are today. The original Superman couldn't do a tenth of what he can today, specifically because a good many of his powers weren't even thought of or invented yet (such as lasers). The original Green Lantern couldn't affect wood with his ring (sonic screwdriver, anyone?). Nowadays, they're practically Godlike in what they can do, as are their enemies.
So, back to your question.
Several times in the comics (and I think once in the original animated series) Magneto has mentioned that his powers were failing (due to age) but to be revived by no less than the planet Earth itself. Magneto has been resurrected at least once because of such (sometime in the 90's) and if this is truth, then as long as he is within Earth's magneticsphere, it could be possible that his 'power' is boundless. Now Magneto has gotten tired many times, and has weakened as well from overuse, but generally he seems to be the Energizer battery. The only real limitation he seems to have is range; which has been inferred to be several miles (back when he owned an island in the late 70's) to hundreds of miles (when he owned Asteroid M).
I haven't kept up with Marvel in quite a while, but Magneto is a classical villain; goal-oriented, driven, sympathetic, but more than willing to step on toes. His dream of giving Mutants freedom and a place to enjoy it justifies his means of doing some, sometimes brutally. Yet despite his authoritative stance, he isn't an evil man, but I'd stay away from him if you got an electronic pacemaker if I were you (and you were a mutie-hatin' human).