Most versions of the original fantasy game on which the G&S rules are based used a single 20-sided die (the 1d20) for combat and task resolution, instead of the 2d10. Some players and BMs might prefer this old-school method over the default one. That is, of course, a perfectly valid way to play Great & Small, but some insight into why this change was made might be helpful in making the decision to switch to a more classic style.
Great & Small aims to capture a reality-lite feel like that reflected in classic works of animal fantasy like The Lion King or Duncton Wood; that is, a world more or less like our own, with animal characters who behave more or less like their real-world counterparts. As such, using 2d10 instead of 1d20 creates a game in which most core dice results will fall within an average range. Dramatic successes and failures will be rare. Lower-level threats would become less challenging more quickly, while making it harder to get lucky and score big against threats that outclass you. Individual skill and training (like character lore levels, or niche dice) can thus count for more and make a bigger difference. Sort of like reality.
However, these "reality-lite" stories are not the only kind of animal fantasy. There are other flavors of the genre, like The Book Of The Dun Cow or the Valdemar stories of Mercedes Lackey, in which magic and monsters reminiscent of classic fantasy role playing are integral to the plot and setting. Players and BMs looking to capture the feel of these animal fantasies could do quite well using the classic 1d20 method. This will create a game in which all possible results between 1 and 20 fall on an even distribution (that is, they each have an equal chance of occurring). Dramatic successes and spectacular failures thus become more common, and lend a more epic feel to the shared story.
The rules for Great & Small work just as well using either method, but groups should be aware of the implications before deciding on one or the other method for their campaigns.
In general, it's a good idea to use the standard 2d10 method for campaigns that feature minimal to no magic or monsters, such as the Legacy Of The Longpaws campaign scheme I'll be describing in the near future.
For higher fantasy settings that recall the classic old-school experience, such as The Trucewood Vale (also forthcoming), a 1d20 method would probably be better.
But, you can also mix & match, using the 2d10 method in combination with access to limited or secret magic and monsters. This "occult" style best suits a campaign like the Creepy Crawlies scheme you'll also be seeing in more detail soon.
Stay tuned to the blog for further information on playable species, game mechanics, details on the campaign schemes, and reviews of some inspirational material.