Alkaline battery
Voltage
Initially upto 1.6v per cell. Voltage drop is approx linear over the battery's life, so life can be estimated by measuring off load voltage.
High power use
Alkalines feature much greater capacity than the zinc carbon battery. However delivered capacity depends greatly on load current with alkalines, and high drain apps dramatically reduce the capacity they can deliver. High drain use leads to short battery life. These batteries are ill suited to high drain use (ironic that they're primarily marketed for this).
For high drain applications, Nicad or NiMH deliver as much or greater capacity with a fraction of the run cost.
Ultra batteries
'ultra' 'extra' 'plus' etc alkaline batts are sold for high power use. These have capacity affected less by high drain to some extent, so last somewhat longer. However the cost is even higher.
Low power use
Alkalines are ideal for low & medium drain apps, where they can give much longer service life than ZnC, and avoid risk of leakage.
Other info
Alkalines rarely leak, so don't cause the damage to appliances sometimes seen with zinc carbon.
Shelf life is longer than ZnC.