First of all, let me just say that I love Arthur. I grew up watching it, and even though I'm 13 now, and way past its target audience, I continue to watch it.
This show was golden up until sometime during Season 15. That's when things started going downhill a bit. It seemed like they were running out of ideas for plots and they just weren't trying as hard. But Season 15 wasn't nearly as bad as the season that's running now. The new episodes are just terrible. The half-assed flash animation looks like total sh*t, the plots are as weak as ever, and it's plain obvious that Arthur and DW are being voiced by the same person due to not differentiating the two voices enough. Not to mention that annoying new character Ladonna who was obviously only brought in to have a plot for the season opener (since the writers clearly aren't giving a f*ck anymore).
I also don't like the way they pair up the new episodes. Usually both episodes will be centered around the same character. It almost seems that Arthur's become a supporting character. I haven't seen any episodes about him lately. They should just rename the show "Arthur's friends who no longer have interesting lives"
I think this show was at its best from 2001-2004. 1997-2000 was great, and 2005-2012 was pretty good. But late 2012-2013 sucks...