I was also someone that didn't think HL2 was all that. I played L4D during one of the free weekends, and while it was fun for a couple of hours it's not something I would have spent $40 on.
Totally. The fun wore out very quickly for me, and I couldn't get it off my hard drive quick enough.
I've said it before: They tried to make Serious Sam, in the dark, with some friends. They failed to make it fun though.