He was supposed to be a one-off for Taker to go over iirc, but Glenn Jacobs was so good in the role that he got 20 years out of the Kane character. Amazing, really.
I'd put The Shield in there. Nexus just leaves a sour taste in my mouth because of how that turned out.
Jericho is the best debut of all time imo, though.
Shinsuke for the initial reaction is definitely up there, and I doubt WWE is going to **** up his booking -- mostly because he's on Smackdown. Maybe he's top-5 debut, it's still too early to say, but it's going to take a lot to top Jericho's imo.
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Was it really that Jacobs was good at the role? I feel like any big man with decent ability could have pulled off the Kane character. It didn't take much. It's not like he was cutting killer promos and having great matches. Respect to Kane for having a 20 year WWE career, but he is probably the most overrated wrestler I've ever seen. 20 years, but what did he actually do? I can't even think of a great Kane match. The TLC match on Raw in late 2002 is all I can think of right now and it's not like he was the reason that that match was so good. The thing people will remember most about him is his association with Undertaker, and pretty much every Undertaker vs. Kane match and feud has been terrible. And I know this is not his fault, but Kane's career has been filled with bad story lines. It's been 20 years, but there's not much that is noteworthy, at least in a positive sense.
His debut was cool but loses points for not knowing where the main camera was when he had Undertaker up for the tombstone.
For me, Jericho's debut is easily #1.
Other ones off the top of my head:
-Lesnar - right away, they made him seem like a really big deal.
-Bray Wyatt - although it was kind of ruined for me by the Husky Harris chants.
-Shield
-Sting - just felt like a special moment.
-Tazz - This was awesome, but I do have a friend that stopped watching wrestling because of Tazz's debut. He knew nothing about ECW and was a strictly WWE/WCW fan, but he got excited about the build to what would be Tazz's debut. But he was very disappointed once seeing how small Tazz was. He was so turned off by it that he never got back into wrestling again.
Nakamura and Nexus was cool. I think we should only focus on the actual debut in this discussion, and not let subsequent booking affect your decision. If Nexus loses points for how they were booked after the debut, then Jericho should too because he was booked poorly for a while after his debut.