Warlock having two slots is a huge limitation, but I find that it is worth the cast for the two Hexblades I've run for a bit.
I also find that warlocks tend to end up with more than just 2 slots at some point - often fairly early, either due to multiclassing or magic items. My most recent warlock is fifth level. He found a pearl of power and built a rod of the pact keeper. His common trend right now is to cast AoA, recover the slot, use a spell in the combat (hex, hypnotic pattern, suggestion) and to reserve a misty step or invisibility if necessary for escape / utility. In a recent battle, he held a choke point and a lage number of weaker damage melee opponents were stopped in their tracks when they each realized that hitting him killed themselves.