I think (from my horrible memory) the SU-30 is an upgraded SU-27 that was developed in the mid '90s. It's a beutiful aircraft that, in my own opinion, was built to fight in air battles that haven't been common since the end of WWII (gun-range dogfighting, turning-n-burning, w/e you want to call it). Compared to the SU-27 I think it has an increased range of up to ~3,000 N-miles, which I think was the SU-27's main drawback (it's lack of range compared to other craft of the time). The SU-30 also has upgraded electronics and such, and it operates with two pilots, much like the F-14 tomcat, which in itself is an edge above other one-pilot aircraft imo.