Caveat: I consider Jay Libby a friend, and I have been commenting on his work over the past decade, but I am also abreast of most of the super hero genre RPGs here on RPGNow and am a 23 year fan of the Marvel Super Heroes game upon which G-Core is based.
First: ICONS, this isn't--if you like your random-roll MSH blended with FATE, stick with that, but if you're looking to revive an MSH style campaign and want to introduce new players quickly, G-Core might be the game for you.
G-Core is "off the grid," using a Stat+ "Special Focus" + d10 vs. opposing roll resolution rather than the classic table. Saves are used to handle situations like Stun, which is a far less cumbersome mechanic than in MSH. G-Core uses character builds with point allocations based on career, origin, etc, basically a nicely pared-down version of Fuzion Blocks. No random roll options here, unfortunately. Powers are purchased similarly.
G-Core packs a lot into 24 pages: a gadget creation system, vehicle rules [which even ICONS doesn't have] and the Scaling System from The Basic System, which potentially allows for the creation of anything from mecha to a Death Star.
Other Selling Points:
The Price: If Jay keeps the price at $2.50 per pdf, the G-Core line can certainly compete with Resolute 2E and other similarly priced game lines.
Cross-compatibility: Your MSH, and ICONS, material should work with G-Core with little change, which is ideal if you're playing with a group who may not be warm to the non-linear aspects of FATE.
The Inconsistencies and Missing "Stuff": As mentioned above, characters are built on a point buy, that is every aspect but Resources, which is randomly rolled.
The list of character types is fairly standard, except there's no pure "robot" type. What if I want to build Optimus Prime's cousin?
Lastly, and this isn't an inconsistency, more of a personal preference: I am a huge fan of lifepaths, and one would think that with Jay's experience with Fuzion that he'd include one here.
I say, if you're a fan of retro-Super Heroes gaming, and of MSH in particular, you probably won't be sorry to have spent $2.50 on G-Core.