The 17-55mm f2.8 IS is amazing in that way something that underwhelms you by virtue of having no weaknesses is. Resale is good, too. And it's sharp and the right set of focal lengths for portraiture and landscape (could be a little longer for portraiture, I like 85mm on crop). Some weird, gnarly CA but whatever... No distortion. Punchy, nice micro-contrast. I liked it for stills and for video. It's the lens I miss most now that I've gone to FF. Build quality was as good as my L lenses.
And to be perfectly honest, I preferred the 18-55mm kit lens to the 17-40mm L on crop. I like the 17-40mm L much more on FF, even though the corners are bad. It is a fine lens by f8 and it's contrasty, but so is most everything else.