But then you have simply copied the Elemental Bolt: Earth, with a more expensive scaling option for higher crits. I think that would be a bit overpowered for an Universal spell.
Ok, maybe make the crit type different, make the scaling cost more, and maybe even have a scaling maximum - like a medium sized crit would be the largest it could go. I just think that having little "special cases" is a way to get a more confusing game. The reason most games have been going for the "everything is done the same way" rules systems, is that the people who play the games want it that way (for various reasons, ease of learning/use being only one).
However, the only problem is if you have a different combat system, for instance, if you upped the "Deadly" to make combat go faster. You would have to up the deadly in Arcane Bolt, or it would be weak and useless. (I would say increase the die size, maybe to d12).
As I prefer H&S, I prefer it to be a little more deadly, but still would much rather it be handled the same way as EVERYTHING else. (Qualify: I do not know every single little aspect of the game so far, but have read over a lot of it, and so far this is the only oddity I have found.)
The idea behind the Arcane Bolt was to create an attack spell that anybody could learn, but that wasn't as powerful as the Elemental Bolts (hence no crit rolls). It was mostly something that dainty ladies might learn to chase away that mugger in the evening...
With the rules as they are, doesn't it take a non-spell user to take the Arcane Power talent to gain the ability to cast spells (or, just go into a profession that has access to spells, right?) - then still have to pay 4 DPs per rank to learn?
Either way, it means that the individual has spent a bit of DPs to learn that spell, so allowing them to get crits with it is OK by me, especially if the crits are limited in their power (as I mentioned above).
Plus, if someone wants to learn how to attack something and they do not have magic, then do what everyone else does - learn to use a weapon. It's all the rage for a reason.