Metasploit is nothing like core Impact. Metasploit is a frame work for expolits, and it well worth having (DCOM on NT4 for example). Core Impact is a whole package (port scanning, service finger priniting, expoliting, and continued testing from an expolited machine), and tries to almost do all the security testing, but just clicking a mouse button. I have seen a demo of it and was not impressed in what I saw. All the things it did could be done by better tools (funny their port scanner worked in a very muck like nmap) as for the exploits most can found if you look hard enough.

SittingDuck