We've had a dragon shaman in our group for over 8 levels now, and the class certainly has its own flavor.
First: forget any hope of ever doing damage. This is not what the class is about. The breath effect is there for kicks, but it will never do significant damage and the 1d4 rounds/use limits it even further. (The main time its useful is when you're fighting things that don't have evasion or immunity to your breath, but are hard to hit normally.) Plus, you get a 3/4ths BAB and no cleric buffs to boost you, so you'll never hit very often and won't do much damage when you do. Bards will out DPS you.
However, you make an incredible meat shield. With tons of Con, a d10 hit die (wow) and full armor and shield (our shaman even took shield-AC-boosting feats) nothing will ever hit you and if it does you'll never go down. This is really important because the entire party will be relying on you to stay conscious for your primary function, which is:
No one will (almost) ever die with a dragon shaman in the party. The healing aura IS the class; that's the best ability they get and they can take it at level one. You'll keep it on 90% of the time at low levels, and it is great for keeping folks from bleeding to death. It also helps fallen folks jump back into the fray. And as for starting each battle at half health - that's actually quite AMAZING. No cleric can keep up with you for healing, because you will never run out of healing aura. Add to that your lay-on-hands ability to top folks off, and you'll heal even better than a cleric out-of-battle (and not too bad in-battle). (Although others are right: you are not a cleric.)
Later your other auras get better, too. The +damage one is nice, and makes you more like a bard in some ways - except, again, bards have a limited (although high) number of times per day they can sing. The bonus to init checks is a GREAT aura to leave on while you're not healing; everyone starts every battle just a little better off.
Overall, the dragon shaman is like a cross between a bard and a cleric, except more useful than most hybrids of the two because they never run out of their abilities. I will underscore again, however, those who have said that this is a support character. Do not believe you'll be turning the tide with DPS - your job is to keep everyone up and ahead of the game.
All that said: the most important thing you can do if you're going to play a dragon shaman is to go out and buy Dragon Magic. That book has TONS of goodies for shaman, and it will help boost and round out your character tremendously. In particular, there's a level 12 feat that allows you to turn on two auras at once - this is spectacular.