I've loved Fire and always will. I liked the randomness of it and how at times you can putter along but on the flip side you burn that target so hard its processor melts along with it. That being said the one thing that has left a rather sour taste in my mouth is Combustion. The first incarnation of a massive crit buff was alright and I think the change to a DoT was a helpful change but I'm thinking it may need a slight tweak.
What if rather than creating a DoT that changes in power depending on how well your Ignite and Pyro are ticking, rather change it to a buff. When activated all damage over the next 5 seconds, random thumb sucked number, is also converted to a DoT on the target that still can then be spread using Inferno Blast. The goal here being to keep the feel of burning your opponent but to remove some of the Ignite munching issues and remove some of the massive variance between a good Combustion and a bad one. The damage should be about 75% of a great Combustion.
This should still separate a good player from a bad one since the best option would be to link all cooldowns, Alter Time and a Pyro so you get the most out of the window period. A bad player would simply use it on cooldown and be less effective.