First, there is a new variant of the SU-27, the Su-35-1, which is supposed to supercruise.

The strakes on the nose of earlier models, and the canards of the later models, both of which increase high AoA agility at the cost of additional supersonic drag have been deleted, but the agility is retained because of the new thrust vectoring engines (NPO Saturn Item 117S). (see vectoring nozzles below)

Additionally, airframe has been lightened, which would increase cruise speed, and about 2000 pounds (about 300 Gallons) of internal fuel.

Also, it looks like the Russians are fitting the SU-27 class fighters with an
AESA radar with mechanical scanning.

This provides something like 2x the area that can be scanned by the radar, and better off sight performance.

One disadvantage is weight, which is why the helmet cued volume is less, because the antenna cannot slew quickly, but there are a number of significant advantages.