The shooting is better in Armageddon, but it's essentially a completely different game. It's hard to compare the two. It's closer to Rage, Lost Planet, Serious Sam or Hard Reset than RF: G. I personally enjoyed it but I like linear shooters.
I'll agree with the shooting part since it's even more important in that game. Armageddon is one of those games where people either love it or hate it and I can understand why some might like it if they don't mind linear shooters, but in comparison to Guerrilla in most categories, it just doesn't match up for me. Like you said, it's a completely different game and that's why a lot of Red Faction fans were turned off to go from an open world sandbox to a more linear game that there's no shortage.
It definitely depends on what people are expecting from it.