There is a lot that I like about the Warlock, but it also disappoints me.
I would like the warlock far more if it mechanically supported doing the sort of cool things that make up the warlock flavor text like summoning planar entitites to make eldritch bargains. But no, the coolest parts about being a warlock basically gets punted off-screen or to the GM. The summoning abilities are "meh." I almost think that you could change the name and flavor text of the warlock to the sorcerer and leave everything about the warlock mechanically unchanged and it would have a negligible impact.
The Goetics in Invisible Sun, in contrast, perform ritualistic magic that summons angels, demons, and spirits to negotiate pacts in return for magical favors, information, etc. It feels like playing John Constantine, Faust, or Elric of Melniboné. It feels like how I imagine a warlock should play based upon its flavor text.