I love Mouseguard, both the RPG and the comic.Burning Wheel is a system I'm curious about -- I've played a version of it with Mouse Guard but haven't tried the original. I will add it to the list of "Grade..." posts.
I don't want to derail your RM thread too much: but BW has some surface-level resemblance, like a long and fiddly skill list, which results in characters with diverse capabilities that are set out on their PC sheets. BW does some basic skill stuff more cleanly than RM: augments (as in, things like how much does my skill in Disguise help my skill in Acting), and untrained tests ("Beginner's Luck").
Burning Wheel does a lot more differently than alike. It's relationship to MG is similar to RM vs MERP... RM has many more skills than MERP, but the ratings and rolling work the same way; MERP also reduced the complexity of the weapons. Meanwhile BW skills and difficulties are comparable to MG, but the skills in BW are much narrower and MANY more - 10× or so as many; the combat rules and details differ, there are many more actions in each of the 3 plotted combat systems than the 4 of Mouse Guard. And each of those is different from the others. The biggest difference is BITs work differently than MG BIGs; MG BIGs are all BW Beliefs, BW instincts are a different thing (essentially a situational automatic macro)... Plus Artha (≈ MG Rewards) has a third type, and there's no BW equivalent to Nature.Burning Wheel is a system I'm curious about -- I've played a version of it with Mouse Guard but haven't tried the original. I will add it to the list of "Grade..." posts.
Nature's not entirely the same, but I think it's pretty clearly an iteration on what Crane was trying to do with the emotional attributes (Greed, Grief, Hatred) in Burning Wheel. I'm not familiar with the second edition of Mouse Guard, but IIRC in the first edition, the end result for hitting the extremes of Nature was somewhat similar to hitting the extremes in the emotional attributes — it's an end game situation for the character.
I've gotten the impression that BWHQ isn't entirely satisfied with how Burning Empires works, though it prefigures some of the work they've done in Mouse Guard and Torchbearer in terms of breaking up play into some arrangement of turns.
MG 2e's changes are few and minor, save one that's memorable and very obvious: Lores no longer have skill levels, and used only for FoRK dice. (My players made extensive use of the option in 1e to use Wises to define things, so for me, that's a suboptimal change.)
I know that ICE (current incarnation) is in the process of releasing their RMU (RM unified) material. I haven't bought any of it, but my understanding is that it is probably closer to RM2 than RMSS in basic structure.
