With that logo design, it is more recent than my 26" Nimbus Muni Frame. Based on this I am confident that the one you have pictured will be ISIS. Given mine from 14 years back is. And yes I agree it is almost certainly a 26" Nimbus II.
I bought mine in 2009, after a recommendation from this site as a good uni to use in the snow.
I still have it and actually even have it with me on holiday, where I have been out cycling it out in the snow. 
Here are a couple of quick views to see the older logos at the front and side.
Notice also the Magura brake mounts that yours is lacking since it is newer and these days things have generally moved on to disc brakes. Indeed if yours is a Nimbus II, it will have no brake mounts at all and if you want a brake you will need a D’Brake.