I like the new system for leveling weapons via heat: it's fun to see items develop, and really encourages people to keep using different weapons as they develop their arsenals.

However, I've noticed that for a given amount of heat in a level, items seem to level at the same rate, no matter how many items are involved in leveling. (my blaster doesn't level any faster if every other piece of equipment is maxed out already)

This is a bit silly, in that heat is an intensive property. If there are fewer items heated, then via the simple relation q = m*C*deltaT, the temperature change / level rise in a single item should be higher when there is less mass (but a constant amount of heat).

Far from being nitpicky, I actually think that making heat gain depend on the number of items would be a lot of fun: it would encourage people to make even more choices. Do they equip their entire new set of gear all at once, or keep some old "complete" gear on, and level the new stuff piece by piece to get special bonus advancements on one thing sooner?

And while we're on the subject of physics: I've noticed that the amount of damage a sword does is totally independent of how many enemies it passes through along the way. Among other things, this means that a single swing of a good sword is enough to kill a dozen pink jellies at once, on the early levels... that's convenient and all, but it discourages the use of mob-oriented weapons, like bombs, by making swords way overpowered. Perhaps the damage could be tweaked so that attacking 5 enemies with 1 sword swing did less damage per enemy?