I must say that I am really impressed by the balancing done in 4e. I like the following classes after seeing them in play: Fighter, Warlord, Cleric, Bard, Sorcerer, Wizard, Ranger, Rogue, Barbarian, Paladin, Invoker.
I haven't seen the Shaman in played and it doesn't look like my cup of tea. I disliked the first incarnation of the Druid, but it might be fixed now. I am undecided about the Avenger after seeing him in play, he sure isn't a high damage striker, but he has a lot of control and single-tank aspects and to him.
I think 4e has done a really good job and there is surprisingly low amounts of cheese available with unbelievable amount of good builds available.
Regarding the bard: being able to move allies out of flanking positions and giving loads of temp hp makes them very good healers. Their at-will powers are really really good. Effectively giving the WHOLE party a +2 bonus to hit a single enemy with an at-will is awesome.
One note regarding the Fighter, I have a Dwarf Battlevigor Fighter in my current group and he is SO hard to take down. He generates ridicules amounts of temp hp and with the level 7 encounter power come and get it/get over here, or whatever it's called he has great control as well. He can switch from a 100% defensive at-will to 100% offensive at-will making no choice "good" against him.
So in short: I think you will find all classes very playable and I am impressed about how little power creep there has been. Overpowered powers have been errataed and new feats and powers added to support weak builds or classes.