Roger at Lensrentals has probably seen more of those lenses than the rest of us ever could (barring a visit to a factory or something), and he's written a nice blog here about the differences between the mk1 and mk2 of this lens, from what I've read there the new one certainly looks a lot better and more robust.
As to whether it's the 'worst', that's debatable, I suppose it's probably the worst 'most popular' one (especially considering the people who'd want it would have higher expectations and would treat it more harshly), but there's a lot more old ones to compare from that noone uses anymore...