All things considered, I've decided to wait until SH5 has been around for a few weeks so I can get some indications that they have made it worth the purchase price and it actuially WORKS this time.
I guess I'm still irritated that the last copy of SH4 I bought to install on a new PC had a ridiculously bad installation routine that screwed up my Registry and tech suport was nowhere to be found after the charges went thru on my credit card.
As to longevity, sequels are nice but bad sequels can ruin even the finest series of anything, from movies to games to wives.
