with wrath and dots its by far the best single target dps of any class, period. Wrath is the highest dps of any ability at 39 alone, and if you spec and glyph for the dots, you are almost likea warlock and can literally just spam dots and own the dps meters.
Having said that, you go oom like no other. No innervate, no regen while casting to speak of, and a mana pool thats just not that hot to begin with mean you can toss out all kinds of damage but if the fight goes on for any amount of time you will go oom and have to run off and drink.
You also wear alot of cloth so you have no real armor, you cant blink and have no shields etc, so you arent the most durable. However your heals are ok and you can always shift and travel away as long as no paladin is usin justice, in which case you are just dead period.
So, overall, nutty insane dps, best single target period, can dot 90% as well as a warlock too, and can travel or stealth etc and can do some minor off heals. Downside being you go oom faster than any class by a mile, and it really gets annoying (if mana usage was more reasonable this would be an insane spec, although its dps is so crazy that its still really good). You also are in cloth and can be fragile, and ret pallies will own you if they use justice.
Mages are not glass cannons, thats just some bs they make up so they can get buffs, i have one, its not true. However, balance druids at 39 are definately glass cannons, they have to sit and take damage, and have no real outs to alot of it. Keep all this in mind but overall I think you will enjoy the spec.