Lightning Bolt is far inferior to Fireball because of game design.
Both spells are the same level, do the same damage, and have the same save so that’s a tie. The only difference is element and area of impact. Fireball is a 20ft sphere of damage, Lightning Bolt is a 120ft line.
Going by that, it seems they both have their uses. Occasionally, the elemental type is useful, but when that really becomes an issue in most games, it’s later on when you have more tools to deal with that mechanic anyway. However, there are a few things in this game that make Lighting Bolt decisively worse in almost all situations encountered in this game.
Level Design. Lightning Bolt shines in long narrow passages where you can blast a lot of enemies with one strike. Such as one may encounter in an actual P&P session in a dungeon, labyrinth, alley, and so forth. I haven’t finished this game yet, but this is rare. Bottlenecks aren’t common as most fights take place in larger rooms or outdoors.
Friendly Fire. Lightning Bolt is inherently more difficult to use in my experience because with Fireball, you just need to be careful where you put the focal point and make sure no one will be in the area of effect once it’s it’s expected to land. Lightning bolt not only requires you to avoid friendly fire, but usually also requires you to spend time repositioning your mage. This typically involves going out to one side which also makes the mage more exposed and harder to support and doesn’t allow for a melee to block incoming enemies as easily.
There is an undocumented inaccuracy penalty with Lightning Bolt that I do not see in the spell description, an inaccuracy which I have never seen in any of the many other similar games I’ve played. The game shows the red line where the spell is to effect, but it’s not uncommon for it to completely leave this area and arc off the the side. I’ve even seen the spell miss by as much as about 12ft (4m) which is just absurd. I’ve seen it completely veer around all the intended enemies and instead hit 2 or 3 of my own people. I don’t know if this is a bug, but it’s terrible and makes the spell garbage.
Is this inaccuracy intended? I’ve never known it to exist anywhere else and I don’t see any references to it in spell descriptions, nor do any other line spells behave this way. It should be greatly reduced/fixed. For Fireball to suck this hard, it would have to be allowed to impact on obstructions (including party members) before reaching it’s destination.
So there you go, Lightning Bolt sucks. Go Fireball. It is generally more effective, reliable, and much safer to use.