I don't even really consider Portal a shooter, it's really more akin to puzzle games than shooters.
As for the Bungie thing, they're not actually owned by Activision so they have some protection there, and IIRC they just have a contract to let Activision publish up to 3 games in their new IP, but Bungie will still own the IP itself. Also IIRC, it's not an entirely exclusive contract, they can still make games for other publishers, Activision just has the publishing rights to 3 games on a single IP.