Here is a good class overview at 70 I highly suggest you check out.
[media]http://www.youtube.com/watch?v=rnO3qSXruUE[/media]
BM hunters are a very bursty class at 70 but easily countered by a rogue. Here is a hunter I found on my server.
http://us.battle.net...ls/Liraa/simple
Rogues with a tazik shocker are very viable when used at the right time
Disc priests are very difficult to kill because of their resil stacking, while shadow priests and affliction warlocks can be powerful because of UA and Vampyric Touch.
Frost mage is another overpowered class because of their shatters (a frostbolt immediately followed by an ice lance w/ fingers of frost up) Which makes a great combo with a rogue in 2s because of the CC capability and the spellsteals.
Resto druids are pretty decent at this level as long as you keep a hot on yourself at all times incase of a hard switch in arenas. Where druids really excel in my opinion is being able to hot and go bear form to avoid mana burns.
Resto shamans are between decent and OP at this level. They are very hard targets to kill and cc with tremor and stoneclaw totems.
Warriors are very squishy at this level and not very OP in my opinion.
Death knights are very squishy but can 2 shot just about any class. Had a dk do 90k damage in a 2 minute 3s not too long ago.
Paladins are slightly underpowered in ret because of the lack of wings. But make it up with self heals. In holy you get a holy power everytime you are stunned I believe letting you go from 0%-100% fairly easy. Prot does alot of burst as well.
I know, this post is just my thoughts in a nutshell but I thought I'd express my opinions.