He did well at Saints and brought the likes of Mane as stated, however he spent 160 million at Everton and was shite. That being said Rijkaard got a side relegated the season before he took over at Barca, so it's never cut and dry that someone will succeed or fail based on their cv(unless they have continually failed of course).
One thing Koeman has got, is a strong personality, something that the Barca dugout has lacked for a few years. The character of the coach in the dugout can often times be a reflection of what's seen on the field. We have lacked intensity and fight since Enrique and we've had two very reserved managers on the sidelines since.