Having watched a few games of Sunderland last season and can say that Henderson was quite clearly a step up from the rest of the midfield - not that thats saying much when you have Muntari, Cattermole .etc. but you could see he was a smart player - not really a game breaker, but a team player. Constantly kept possession, waited for the right moments to pass, cross. I think he will only do better with better players around him, so before any one judges him, wait a season and see how he performs, I have a feeling he'll surprise alot of you.
That being said, I still think he's been bought for too much (I know even for english players) - 16mill or 20mill which has been reported. Liverpool could have picked up better players for cheaper, but if thats the direction in which Comolli and Dalglish want to go then fair play to them, its good they're sticking with it and targeting players like Jones, Dann, Wickham - however I think the money can be attributed elsewhere as some home grown youth players are coming up at the moment from the academy and theres no real obligation to buy homegrown talent.
In 6-7 years time if Henderson is still at Anfield, then that money will be deemed to be well spent. I would love for him to make an impact at Liverpool and I hope he does as I do rate him, but I do have a few doubts which hopefully can be proved wrong.