Druids are jacks of all trades, master of a few.
Their evocations won't make you forget a wizard, but they will get the job done at a basic level. They can get the job done if there is no wizard, but you'd still be ebtter off with a wizard.
Their melee combat ability won't make the party fighter feel unneeded, but they can hold their own in a battle with a decent CR monster.
Their missile combat is fairly weak, but they have spellcasting to fill that role.
They can heal. If they find they need more combat spells and less healing they can switch that healing out for summon creatures.
They are the best scouts in the game. No other class has spot and listen as class skills with such a strong reason to maximize wisdom.
They have a plethora of defensive spells and utility spells.
They can create a small army on a whim. Summon a few animals, animal growth on them (and yourself in wildshape), barkskin/stoneskin on you (and your animal companion), etc .... A druid can expend a significant portion of his power in a few rounds. They have a knack for stacking spell effects on spell effects and creating bigger effects out of the result. People have not really begun to appreciate the full use of share spell with the animal companion.
An idea that sounds fun to me is the mounted druid. Use your animal companion on a mountable creature and then use share spells to share some nifty abilities with it (while it is constantly within 5' of you).