That's not I V Vi IV (the supposed most popular) but a I Vi IV V

Definitely like the progression...love the shift to a relative minor (I Vi) G em, C am, F Dm etc I use it a lot to create tension in a line before a hook....where someone might expect say a G, but you serve up the Em, then replay the melody line to resolve on G

so say G C D G might be the line, you go G C D Em, G C D G .... you can also double up on the Em to eliminate the second g, so move right to the C

If writing ever becomes work I think I'm going to have to stop