Kantor, nothing freaking fits your criteria.
* is a famous series
* is on a decline
* has an earlier entry that will be on many member's lists
* has only one main competitor which is more popular and more realistic.
Only sports or car games come close but not them either. I'd say Need for Speed but that hasn't got a more popular and realistic competitor.
I'd say PES but someone mentioned it already.
It is clearly Tony Hawk. Skate is the one competitor.
No, you said it already but Kantor was silent like a mouse.
Plus I wouldn't think Kantor would claim that Tony Hawk is "a very famous series, which was once great and which has now gone to crap."
"one particular (earlier) entry in the series will feature heavily in these lists".