ID is kind of like those movies you loved as a kid. They haven't withstood the test of time that well, but for nostalgia sake alone you still have to given them your patronage.
This isn't to say that ID isn't still technologically impressive, my guess is that this will be another astounding engine. Its because of that that they may be the single most influential game developer of all time.
....maybe its not like buying the old movie you liked as a kid, maybe its like going to see a Scorcese film. You know that he hasn't been as good as he was back in the old days, but you still have to respect him. Or maybe its like Ingmar Bergman. You know that even if you don't like it at face value, your supposed to like it for technical reasons.