I've been watching all Nintendo E3 showcases since the Gamecube reveal, one way or another. Never missed one.
Honestly, if you had the correct mindset, they weren't that bad? By 2008, we all knew what Nintendo had in store and that showcase was them just showing it. Honestly, i liked the Wii-thing games a lot, so i enjoyed it quite a bit.
The E3 2015 was Nintendo trying to save face for the Wii U. I had no issues with the content itself, but the pacing felt like a miss, i did not expect developer interviews in the middle of an E3 direct, and they used them to pad the show way too much.
I had more issues with the Wii U reveal show, that was... a bit of a disaster, more than anything because of the first party tech demos shown that were... minigames, and New Super Mario Bros with Miis. I remember understanding that it was a new console and later tech demos confirmed that it was in the ballpark of PS360, but it was really easy to miss it thanks to the show itself. Even my sister called me, completely confused, to ask me what the fuck was the Wii U.