I really find this system to be interesting from a pure mechanical perspective. For those that don't know, Alternity, instead of using 1d20+bonus, uses more dice instead of that bonus. So a fighter with 1d20+4 to attack would instead roll 1d20+1d8.
I've been contemplating the consequences of such a change in basic mechanics. In DDO, for example, at high levels any AC less than 60 is about equal to AC in the 20s precisely because the bonus to the roll totally dwarfs the d20 result, so AC 50 and AC 20 versus a +50 attack bonus is still 95% chance of success. But if that +50 was instead a d20+d100, there's still the chance of rolling low on the d100 and AC 30 being more useful than AC 20.
The only downside is such a system would be a hassle to play using actual dice. For starters, d14s, d16s, d18s are all specialty dice. And adding 1d20+2d12 has significantly different results than 1d20+1d24. Even more granularity could be added to the system with odd-numbered dice, but these dice are also specialty dice (even if you're using a 1d6 with two of each 1-3 for a 1d3), and can only be simulated up to d5 with standard dice, though still at some difficulty.
Still, if these problems could be overcome, perhaps with a computer-aided die roller, I think it would give room for much more variation in power levels while sticking with a relatively simple (1d20+more) system like D&D. No more, "It's impossible to miss" scenarios. But I guess it still can put some target numbers out of a character's league.
What are your thoughts? Is there a game system you like that allows a wide variety of power levels?