Dalamar said:
My overall impression is that what the warlock loses in overall efficiency, it gains in lasting power and flavor. A really nice class to play. And Repelling Blast on a Huge creature makes for a great visual
I'll agree with the first part, but point out that Repelling Blast only works on Medium or smaller creatures. Which serves as a reminder that Invocations need to be read carefully.
I've been playing my warlock a month and what strikes me most is that the class if one of the few that isn't a derivation or combination of the core four classes. Warlocks usually end up as light ranger fighters with a selection of magical enhancements. They're really very modular. Instead of a selection of spells you have a very few invocations on call to support your concept. You can go stealthy infiltrator, mega-face, hexer, summoner, mobile sniper, or battlefield support. (At least, those are the main ones that come to mind.)
With so many more Invocations available compares to those any one Warlock will have, it's impossible to say what to expect of the whole class. With no ability to switch spells, once they have a PC built you should be able to know everything they can do. Conversely, with Invocations being at will, expect them to be do it at every chance. Baleful Utterance? Every lock gets Shattered. Fell Flight? Pits and cliffs are not obstacles. See the Unseen? No invisible assassins, ever. Warlock's Call? Expect them to carry on entire conversations with distant friends and keep the entire party in contact.
So besides another reminder to carefully read the Invocations and how they're different from spells they mimic, my real advice is not to try and know the Warlock class but know your player's specific Warlock. He won't have many tricks but he'll use what he has freely.