It's worth comparing this spell with Otiluke's Freezing Sphere (PHB 263).
[TABLE="width: 500"][TR][TD]
[/TD][TD]Delayed Blast Fireball[/TD][TD]Otiluke's Freezing Sphere[/TD][/TR][TR][TD]Spell Level[/TD][TD]7 evocation[/TD][TD]6 evocation[/TD][/TR][TR][TD]Cast Time[/TD][TD]1 action[/TD][TD]1 action[/TD][/TR][TR][TD]Range[/TD][TD]150 feet[/TD][TD]300 feet[/TD][/TR][TR][TD]Components[/TD][TD]V,S,M[/TD][TD]V,S,M[/TD][/TR][TR][TD]Concentration[/TD][TD]Yes, 1 min[/TD][TD]No*[/TD][/TR][TR][TD]Blast Radius[/TD][TD]20 feet[/TD][TD]60 feet[/TD][/TR][TR][TD]Saving Throw[/TD][TD]Dex, 1/2 dmg[/TD][TD]Con, half dmg[/TD][/TR][TR][TD]Damage[/TD][TD]13-22d6 fire[/TD][TD]10d6 cold[/TD][/TR][TR][TD]Portability[/TD][TD]Dex save to handle safely[/TD][TD]Safe to handle[/TD][/TR][TR][TD]Special Effect[/TD][TD]Ignites flammable objects[/TD][TD]Freezes 30 square of water[/TD][/TR][/TABLE]*Does not require concentration, but will detonate after 1 minute.
Looking over that, I would be inclined to take the freezing sphere over the fireball. Yes, there is lower damage, but it has far greater range, does not require concentration, is safer to move, and requires a lower spell slot. There is nothing stopping you from making a level six sphere in one turn, a level seven the next, and then using a sling to fire both at your foes. It can even help you traverse water or impede the movement of swimming foes. The biggest downside is that the thrown range on it is limited to 40 feet, placing you inside the blast radius. A sling boosts this range up to 120 feet. Additionally, less monsters are immune to cold than to fire, making it effective against a wider range of creatures.
Unless I was going against a foe that I knew had no fire resistance, was in a very enclosed space or had no minions, and I did not require concentration for anything else, I would choose the freezing sphere every time. And if I really needed to simply blast something right away I would still have the regular fireball spell.