I was pretty mixed on the whole affair. I thought the Splatoon & 3DS tech demo sections were pretty flat (not helped at all by not being able to follow which characters were on which team since you couldn't see their names). I completely tuned out during the Mario Kart & Smash sections, especially since Timed doesn't really do it for me. I did like the Retro sections that weren't Balloon Fight, though.
The Mario Maker section was funny in that "let's watch these 2 dudes get continually punished and trolled" sort of way and it DID work very well as a competitive game, but at the same time I didn't see anything particularly new there. ROM hackers have been making bullshit, trolling Mario stages and putting them up online for years, if not decades. It's cute, but I was hoping to get some hint of an actual campaign structure from quality level designers that I could really latch onto. Instead, we saw I Wanna be the Guy. That's not so appealing to me. Maybe we'll see more traditional Mario stages on Tuesday.