I like roll up systems better than roll under. It just seems fundamentally off to me to want a low number. It gets really wonky when a counter-intuitive mechanic is added in, such as when an opposed roll looks for the highest roll, while staying under the target (I've seen so many systems; I wish I could say what it was--probably a BRP derivative of some sort). I get the logic, truly, but this reminds me of some encounters I've had with mentally unstable people over the years: do you want me to roll high, or do you want me to roll low? Make up your mind! Roll up systems make you feel like you're trying to reach a goal, at least, so I'm cool with that.
I'm somewhat lukewarm to dice pool systems, with the exception of the excellent Ubiquity system--I went over this one when I talked about player facing rolls. Most dice pool systems have a couple of problems for me. For one, and this goes to success-based dice pool systems, it seems anti-climactic to roll 10 dice and come up with a result of "three." The feeling is almost akin to roll under systems. Roll up dice pool systems (decried by many) are better, but if I have to add up a ton of numbers, I'd rather it be for damage than to find out if my character "made it up that wall." I think the Cortex system hits a sweet spot for me--attribute die, skill die, trait die, roll up.
I like roll-keep systems. I can't pinpoint why, to be honest, but I can say with all honesty that I've always loved the most popular roll-keep style games, including John Wick's L5R and 7th Sea games and Shane Hensley's classic Deadlands. Of course my recent go-to system, Savage Worlds, is a simplified roll-keep concept as well.
Over the years, I've lost interest in single-die systems. There are three I love, though: Mutants & Masterminds, Unisystem, and Gumshoe. But this is in spite of the single die. (M&M is my all-time favorite supers game because it does everything Champions ever did with relative simplicity. Unisystem is the home of my all-time favorite, if ill-fated, modern urban fantasy setting, Witchcraft. Gumshoe stands, in my opinion, as the best investigative game engine ever conceived.) When I roll a single die, I often get the "you mean that's it?" feeling. I have no other explanation. I could go on about dice curves and probability and such, but honestly, my feeling toward single-die system seems purely emotional to me.
Speaking of innovative dice mechanics, I've been checking out Dragon Age from Green Ronin. Powered by GR's new Adventure Gaming Engine (AGE), it uses three six-sided dice for resolution and d3s and d6s for damage. Like BASH!, the fun stuff is triggered when you roll doubles, but this is particularly in combat and spellcasting. I said you roll 3d6, but one must be a different color. This is the Dragon Die. When you roll doubles on an attack or a spell, and succeed, the Dragon Die result is the number of Stunt Points you receive to modify what you're doing. Combat stunts can range from an extra damage die to knocking the opponent prone to adding to your defense. There's more you can do of course. You can even use multiple effects if you have the points. On its face it seems very exciting, reminding me of those times in fiction when the protagonist sees an opening, perhaps getting lucky, and takes it, to staggering, climactic effect.
There's been a lot of talk over the years about RPGs that penalize players for being innovative (most of them, really). If you want to do this extra thing or that cool thing, there's a penalty to your roll. To me, this Dragon Die/Stunt Points mechanic seems to mimic fiction better. It neither rewards nor punishes innovation, but relies on providence, much like the hero in a story.
I do have one concern about AGE, and this comes more from my board game experience than my roleplaying experience: analysis paralysis (taking too long to make a decision). The stunt system in Dragon Age has the potential to stop a table cold as a player peruses the stunt table, like a restaurant menu, for the perfect stunt. I think if the issue occurs it will most likely be a temporary one, as folks get used to the system.
Tonight I get to find out, as I'll be running the game for family and friends. Two of the players are kids, a pre-teen and an early teen, so I'm excited. I'll report back here about the experience at the table.