Why would you ever get Burst weapons?

[Orm]

There's nothing in the description that says you need to be in contact with the weapon in order for it to remain aflame. Once you've commanded it to ... er, flame on ... it'll stay that way whether you're handling it or not.

Fine then. So that´s just the way we play it. Anyway, I would never like to carry a burning weapon with me for a prolonged period of time.

Right now I´m playing a rogue10/fighter4/deepwoodsniper5 with a frost burst bow and a ring of spellstoring (hunter´s mercy). As a sidenote, in our group keen and improved crit still stacks. So for me it´s 18-20/x4. That happens quite often
It´s nice to see the DM´s face in those moments

 

[Elder-Basilisk]

Actually, burst weapons are better than normal energy weapons in the face of energy resistances. Most resistant creatures have resistance 5 or 10 to multiple energy types. Thus a frost, shock sword will have a 1 in 6 damage of dealing either one point of frost or one point of shock to the creature with resistance 5 to both and no chance of doing anything to a creature with resistance 10 to both. Not too impressive. OTOH, a shocking burst weapon has the 1 in 6 chance of dealing a point of damage on a normal hit and will usually deal more significant damage to the resistance 5 creature on a crit. Against the resistance 10 creature, an x2 burst weapon has a chance to deal damage on a crit and will usually deal damage if it is x3.

Of course, that's still not very impressive. However, it does get interesting on a crit-focussed character wielding something like a falchion or a scythe with improved crit, power crit, and keen (if it's ruled to stack).