As a 70 boomkin, I personally love it. Perhaps I've played way too many other mmorpg's as a melee character so it's a welcome change but it is definately worth trying.
For leveling balance you'll possibly end up what I do open with starfire, moonfire, entangling roots and insect swarm. Generally you'll open up with a decent enough amount of damage to start and when you end that series of spells you can just nuke with wrath. I have a macro that I use that looks like this.
/castsequence reset=target Starfire, Moonfire, Entangling Roots, Insect Swarm If you have Nature's Reach you generally have enough time to get roots off w/o getting hit, but if you do get hit its about one hit and then you just back up and nuke with wrath. About the only problem you get yourself into with this is you can go oom since you'll more than likely lack the Dreamstate/Intensity build right away since you're a lower level. So you can supplement this problem by using Innervate when you're CD caps or just start getting used to using water.
But as for instances and raids go. You can't really expect to top the damage charts, it's possible at lower levels but once you hit outlands it becomes a lot harder. The main thing you'll be best at is supplying a decent dps and a 5% crit rate for your spell dps buddies which is insane on some mages.
Build! Ok heres how I am
here. And here comes an explanation.
Imp Nature's Roots is pointless you'll hardly ever be getting hit by things excluding horde if you're on a pvp server, but for the most part its rather pointless to have. Taking up Balance of Power is important because 4% chance to hit is a lot easier to get in 2 talent points than in gear and with the reduction of 4% chance of spells to hit you thats also nice.
Now in the resto side of the tree it's kind of up to your discression. I personally go with Furor because thats an instant ability to shift into Dire Bear form and Bash someone for a quick 3 seconds to get away or set yourself up a little better. Natural Shapeshifter is also a must incase you find yourself in a situation where you need the extra stamina from Dire Bear Form or you're under fire in an area that you can't use travel form so you shift to Cat Form for a lot less mana.
And finally of course 3/3 in Intensity, because any mana regen is the best mana regen. This also goes with Dreamstate because the two coupled together is so nice to have. Unless you're doing something crazy and you have to just bomb out the spells on a boss you generally can make it through just Starfiring w/o dropping below 50% mana.
The build sort of leaves you with one point to allocate how you feel possible. You can put it into Treants if you wish, but I think its too costly for your mana pool and way too reckless, so I put them into Subtlety to drop your threat a little bit. In instances it's pretty damn easy to pull threat if you open with Starfire and Moonfire on a mob and they both crit.
Hope this works for you.