I thought SHAFT was always pretty popular, at least within my circle of friends.
SHAFT is popular right now because of Bakemonogatari, which inexplicably appealed to way more people than it "should" have.
Yeah, Bakemonogatari is one of the very, very few shows that actually deserve its popularity - but I didn't expect people to appreciate it that much.
The problem is people who only saw Bakemonogatari and Ef, and base their expectations of Shaft shows on that. Most of them will probably be dissapointed with new Shaft productions, while some may actually appreciate the studios strengths. Probably not much of them though, as most of the anime audience doesn't give a shit about direction, or visuals outside established norm. Even if current(well, not anymore) Shaft style will get popular, by that time Shinbo will be doing something else.
Anyway, back to Arakawa Under the Bridge - at first it seemed like it could be another Bakemonogatari, but that was quickly and thoroughly dismissed. Short "episodes", focus on comedy, doesn't take itself too seriously, isn't "cool", but still doesn't seem to be completely shallow. I liked it very much.
Some high points: music was very good, I usually don't pay that much attention to music in anime, but this time it really stood out. Great cast, I think my previous post showed my love for Maaya Sakamoto clearly enough, but Hirou Kamiya really surprised me - I like his voice, but this time it wasn't about his voice, it was about his acting. He definitely grew since voicing Itoshiki Nozomu, with whom Ko will undoubtedly be compared .