When Person of Interest started, I thought about dropping it because of the case of the week format, but decided to stick with it just in case it became arc heavy.
Whereas lately I'm coming to miss case-of-the-week storytelling. I think arc-based stories have perhaps been taken to too much of an extreme. It's good to have characters growing and events having consequences, but it can be overdone.
One trend in particular I've noticed this past season is that because of the need to keep the overall storyline moving and changes happening, nobody seems to be able to keep a secret for very long. On Smallville, new characters discovering Clark's secret superpowers was something that happened maybe once every few seasons, but so far in the first season of Arrow, a new person has discovered Oliver Queen's secret identity roughly once every four episodes. And while in the original '80s Beauty and the Beast, Catherine was able to keep Vincent's existence secret for two seasons, in the new series they've both been absolutely incompetent at keeping their life-and-death secret from anyone in their lives, so that now, near the end of the first season, there's only one main cast member left who doesn't know about him. It's really kind of ridiculous. Sure, the approach in old, strictly episodic shows where such secrets were kept forever could be just as ridiculous, but both extremes are problematical. As with most things, I feel there's a happy medium somewhere between the extremes.
I'm also getting so sick of the formula where every case of the week the characters encounter just happens to resonate with whatever's going on with the main characters' story arc at that particular moment. It got so bad on Fringe that the main character even commented on the coincidence once, wondering if there were some cosmic significance to it.
I don't want arc-driven series to go away, but I think it would be nice to have some variety, to have the occasional series that was mainly about the crisis of the week. Not something like in the '60s and '70s where nothing that happened in one episode was ever mentioned again, but something more like shows in the '80s, say, Star Trek: TNG, where the focus was on the individual adventures but there was continuity, where an episode could have consequences down the road and characters' relationships evolved over time. I think the most recent show I watched that came close to that was Flashpoint, though it had its share of serialized character threads.