To start with, the box itself is nice. Solid, with nice artwork. Inside is a clear plastic insert to keep the contents from bouncing around too much. Roughly from top to bottom, I'll now go through those contents.
First are the dice. Ten solid six sided dice with engraved symbols, black on off-white. Three sides have a snake eating its tail for the cowards, two sides with crossed daggers for the regular successes, and one side with the Black Axe for the "6" side that can be exploded using fate points. While certainly not necessary, these look very nice.
There are five "mouse pawns" in different colors. These are oversized soft plastic chess pawns with mouse heads on top them. They resemble the pawns Gwendolyn uses in the comic to mark Guard patrols on the map. They don't really have any game function, but could make for a nice prop.
Next up are the cards. Three Action Decks, one deck of Conditions, and one of Weapons. Every card has an illustration and rules summary. The Action Decks have three each of the four different actions. The Conditions Deck has three each of the different conditions. The Weapons Deck has two each of ten different weapons, and one card for the mace introduced in the New Rules New Missions booklet. These cards seem to be the most useful things in the box, and I can see them coming in very handy when playing the game, especially with people new to the game.
Next is the rulebook. This is a softcover version of the rules, but otherwise identical to the hardcover book available separately.
Next is the "New Rules New Missions" booklet. The new rules introduce a variety of specialized "weapons" (really tactics and gear in most cases) for different types of activities, from giving speeches to fighting larger animals. There's also three new towns, a Combat Matrix revised for clarity, and rules for using mounts.
The bulk of the booklet is taken up with three new missions, each with new character templates. I've deliberately not looked too closely at these, but they are comparable in length to the sample missions in the rulebook.
The end of the booklet consists of a description of the other components which can be found in the boxed set. One thing I noticed here is that it mentions the presence of "other cards" beyond the decks I mentioned above, specifically cards with conflict disposition, conflict skills/action, and action mechanics on them. I can find no such cards in the box, and they aren't mentioned on the back of the box. I don't know if they're missing from my box or simply were dropped from production, but I suspect the latter given that they aren't mentioned on the box.
Next up are two pads of sheets. One pad of character sheets, and one of GM sheets. The former are what you'd expect from a character sheet. The latter has one side for summarizing the player characters, and the other is a rules summary.
Below the pads is a 3 panel cardstock GM's screen. It looks like it contains useful information, but I'd have to use it in play before I could fully evaluate whether it's well designed or not. The outer side consists of two panels of artwork, and one of information for the players, which is nice.
Finally, there's a map of the Mouse Territories in 1150. This is the same map found on the inside covers of the hardback rules, but with a little more color.
Overall, this is a nice set. Should you get it if you already own the rules? That's a tough call. If you're only interested in "crunch" then $70 is an awful lot for 44 pages of new rules and missions. It becomes a better deal if you're also interested in the play aids, like the cards and GM screen. If you were considering getting a second copy of the rules anyway, just to make things easier at the table, then definitely consider getting this set instead.
If you don't already own the rules, then I'd find this set an easier recommendation. You're still paying $35 above the cost of the hardcover for all the extras, but they are nice extras, and should make playing the game easier.