I liked Infinity Siblings a lot, too. It's a tough wait for the next one, and here's hoping the third one is still coming after Starlin's spat with Marvel. Of the first three OGN's I liked Relativity the best, there was some good stuff with Thanos taking on the souped up Annihilus. Revelation had a fun gimmick I won't spoil here, but past that not a lot happened (besides some meta commentary about how little sense Marvel's continuity makes now).
I can't remember which book had Thanos take on the Annihilators, but that was both brutal and pretty funny.