Cyrillic wght: 900 | wdth: 100 | slnt: 0 | GRAD: -50 / 0 / +50 | opsz: 144

Some of the features found in Cyrillic are a consequence to design decisions made in Latin, seems like in opsz 144 wght 900 they become especially prominent.

1.
In Latin
Р looks wider and brighter in counter than О.

So in Cyrillic
БЬЪ also look slightly wide comparing to О.
Ф looks bright in counters.

2.
In Latin
М looks wide and dark in comparison to everything else.

In Cyrillic
Same: М looks wide and dark. LC м doesn't stand out so much as UC. Also И and и look pretty dark, again n LC it's present to smaller extent.

3.
In Latin
UC is pretty narrow comparing to LC. I realise this is a design future.

In Cyrillic it becomes more prominent.
There are some situations where UC and LC skeletons are the same, but proportions are very different. I think the most noticeable case is Вв (see word Введен). I think -в is overcompensated in width. The group вьъы is wide, while я seems to be closer relation to other letters with dense skeletons (a,e,з).

4.
In Latin a significant group of letters have thinner "horizontals": О,P,R,D,J,U. This helps О not to stand out that much. In Cyrillic this feature is hard to apply to a whole group of letters, as many of them use horizontals close to bar of H weight. This makes letters like О and С stand out pretty significantly in Cyrillic. They have less presence in text in comparison to other letters. This affects ЭЗЄ as well.
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Strictly Cyrillic observations:

1. Лл - I wonder if terminal of the leg can be a little longer in order to read better.

2. I would give more weight vertically to breve.cyr and breve.cyr.case. This is one of the cases where angular terminal becomes even more noticeable. Looking at how strong visually the straight terminals of ЭСЗэсз are, I wish breve.cyr and breve.cyr.case would have horizontal terminals too.

3. г could be a little narrower in order to decrease the gap.