Flame's particle system reminds me of Maya's Dynamics because both were really great when they came out and haven't been touched since.
Flame tried to alleviate this to a minor extent by adding particle presets. These presets are nice, but they also underscore how difficult and limited the particle system is. When you load one up you generally get a reasonably nice effect not to dissimilar from the old Particle Illusion ones (albeit without animated sprites, which is a big deal). The problem shows up when you need to tweak said effect at all. Now you're wading through convoluted expressions and manipulators that don't scale well and are slow to update.
I think the best example is getting particles to fade off. The expression is "transparency = lifetimeI", which is pretty straight forward. Particles will be born at full opacity and fade in a linear fashion over their lifetime. What if I want them to fade up for the first, say tenth of their life? Now i've got some math to do, and quite honestly I don't know how to write that expression. I wish I did, and likely I should learn, cos a little bit of fade up is a nice thing for most particle effects. Either way, it's a bear to do.
Adding turbulence is even more complex. John Montgomery has some great tips at FXguide, but shivers man, that's a lot of code to memorize to get particles to do pretty much the first thing everyone wants particles to do.
I'm upset about this because I think Flame's future is in the commercial space, and the commercial space requires two things: flash and speed. Particles are like lens flares: they make everything look more expensive. People love particles. They're such a great way to spice up a boring pack shot or end tag. They season other effects so well. A few months ago a client asked me if I could put particles on their endtag. We had about half an hour before delivery, and I knew I would have to spend at least that time messing around with different functions and manipulators to get anything even remotely worth looking at. I want a new particle system so I can answer "yes" to that question and send the client away amazed at what me and the flame added to their commercial.
So please, update the particle system. Please. After effects kids and their $400 Particular plugin are snickering at me.
What I would like to see:
1. A vast increase in speed. Video games (video games!) have better, faster particle systems (and hardware shading, if we're being pedantic). I want millions of particles and superfast interactivity. Autodesk employs a large portion of the particle software brain trust (maya, max, soft), so talk to them. I'm using a flame; it's renowned for it's speed, so make the particles impossibly fast.
2. Ramps for controls. Ramps to dictate size, transparency, how much forces effect them, speed, color, etc.
3. Simpler, easier to manipulate forces. Specifically turbulence, and preferably with a few different noise patterns in it for different turbulences. There's a texture set for Cinema 4d that has all kinds of different noise patterns and it's fantastic. While that doesn't directly parallel, the fact that most software have only a few turbulence patterns is weak. Go crazy on the turbulence.
4. As a counter point to #3, I'd also like more complex controls. I'm not sure if the current system can't do per-particle or birth expressions, but they'd come in handy from time to time.
5. Animated sprites/per-particle slips. Old Particle Illusion (and Combustion, and Motion...) get almost all their "wow" factor from the fact that the 2d sprites animate per-particle. This needs to happen if only because it was in baby-flame SIX YEARS AGO.
6. More particle types. Multi point and multi-streak would be a start.
The one thing I don't want to see is a few new features, patches onto the existing system. Flame, and specifically Action already feels super cobbled together (hello action transfer modes!). I want to see a full on re-write, re-think and re-integration of how particles can be used in flame. It would be a cash cow the PR people could milk for years, so fucking get on it!