Even though I have worked on a large number of M4s (the military ones), I could never warm up to it, and don't own any civilian AR. But if a Colt M4 were offered to me at $699, I'd snap it up as an investment, if for no other reason.
If it isn't the "naked" OEM version (no furniture, trigger guard, rear sight) then you got a screaming deal. That version alone goes for between $699-$749 depending on vendor.
I bought a Colt LE6920 back about two years ago. At that time wally world was selling them for $1059 without taxes. 2 20 round mags blocked with a spacer, carry handle and no rear sight to mount on the rail. sling and cleaning kit. this was right around when the Sandy Hook school was attacked. Only difference between mine and yours is that you got the rear sight minus the carry handle. And I got the carry handle. But since the carry handle isn't a big buck item, yea i'm thinking you got a good deal.Frank