Built by Iran — possibly with Russian and Chinese help — the rockets were first shipped through Syria to the Hezbollah militant group in 2002. Today, an unknown number are now in the hands of Hamas. (Presumably, that's thanks in part to a porous border between southern Gaza and the Sinai, now controlled by the new Islamist regime in Egypt.) The rocket is liquid-fueled, has an estimated 45-mile range, and is fired from a mobile launcher. And while it's more powerful than anything Hamas had before, it's still unguided and not particularly accurate — the rocket could land anywhere within a one-kilometer radius of its target. But where the Fajr-5 is short on accuracy, it's a significant boost in destructive power: the rocket can lob up to 200 pounds of high explosives.
Recent reports that the rockets are now aimed at Tel-Aviv and Jerusalem are a bit troublesome. Tel-Aviv is not necessarily a small city but it is densely populated, with large groups of people living in high-rises and small apartment buildings, many of which are jammed pretty closely together.
Then again, Israel's military technology is some of the best in the world, so airstrikes and rocket attacks in Gaza probably have a similar effect, if not more devastating. Comparing the damage isn't really helpful: the bottom line is that, either way, people are losing their lives over this conflict.