Part of it is the vocals. Lately I've seen Danny become more empassioned and just sing HARDER. This translates very well, and I like it.
The video effects have steadily grown in both quality and quantity. This, too, I'm a fan of. The Dragon Dance is probably my favorite NSP moment ever, now.
On the critique side, and I hope Danny/Brian read this-- Lately, many of their songs have approached an Owl-City like homogeny. Not to say they sound like Owl City, just that within Owl City, many of the songs sound the same. I've noticed this with NSP songs-- many of them sound very alike in both song and manner of singing. I worry that if you stripped them of their videos, they'd become yet less distinguishable. And that's not to say they all sound alike, either. It just falls a little short when you compare, say, Unicorn Wizard and Dragon Slayer and Terrible Party against I Just Want To Dance and No Reason Boner.
Finally, some of the phrases Danny uses. Like, just before the chorus, preluding with "Oh Yeah" (This song, Dinosaur Laser Fight, etc) -- It feels like filler. And "In case..." 2/3 of the way through the video when his first attempts to woo the girl fail.
Danny, Brian, I love you guys. I'm so glad to hear you've achieved this level of independent comedy, Danny. I can't wait to see your next video, I can tell you'll be able to put your all into it now (which is not to say you weren't before, just, now there's more all to give!)