Having never seen the Eldritch Glaive invocation in play, I can only offer my observations of the invocation's description and this topic. At first, it looks godly powerful. A Warlock being able to make multiple attacks, each touch attacks, and dealing Eldritch Blast damage? Don't mind if I do!
However, upon further inspection, it's powerful, yes- but the reason it doesn't seem TOO powerful is because of how hard it is to use, realistically. First off, it's a full-round action- meaning in order to use it, you have to start off with an enemy within your reach (or within 5 feet of it, with a 5 foot step)- so unless you're starting off right up in the enemy's face (which is never a good place for a Warlock to begin with), you aren't going to be able to use the feat. Not only that, but sure, it looks awesome when you compare it to a Rogue getting sneak attacks on every attack with Wraithstrike- but, if you recall, Eldritch blast has ALWAYS been a touch attack, and it has ALWAYS done the same amount of damage as it currently does. And yet, nobody's complained about the Warlock being able to blast from 250 feet away. How many rogues can get a sneak attack, even one per round, from 250 feet away? None of them. And yet that wasn't an issue before.
So, anyway, like I said, the invocation looks hella powerful- but in order to use it, you have to be in quite an unadvantageous position to begin with, which can limit its power significantly. True, Rogues don't have all of the advantages that Eldritch Glaive gives a Warlock, but then again, Rogues do more than sneak attack, right? (I'm talking about skills, Evasion, Trapfinding, etc.)
It seems to me that all Eldritch Glaive really is is a way for a Warlock to finally be a competent damage dealer. Nobody's complaining about the Sorcerer being able to shoot off Scorching Rays that blast everyone to kingdom come from a range, or the Wizard firing off quickened Fireballs or whatnot. The Warlock is still just as limited in all of his abilities as before- the only difference is that now, there's a somewhat possible option of being somewhat competent damage-wise.