Although I didn't really like the original SaiKano series much, I decided to try out this OVA series anyway just to see if it added anything new or interesting. But as it turned out, I wasn't much crazy about this one either.
The show did have a few good points. For one thing, you got to see some things that were only hinted at in the TV series. For instance, you get some brief information about how Chise was created, and you also got to see more of her fighting in the war. Also, the OVA series thankfully cuts back on the number of blushing characters, which was a chronic issue for most everyone in the TV series.
But although the OVA seemed to improve on the TV series in some aspects, overall it didn't added anything to either the story or the characters' development. Instead, it focused mostly around Chise's obsolete predecessor -- Mizuki who was the prototype "ultimate weapon" and had outlived her military usefulness.
The story drew a parallel between the Chise and Mizuki who were both trying to overcome their instinct for destruction in order to find true love. But I had the same problem with both series: that being the discrepancy between Chise and Mizuki's super destructive capabilities versus their weak personalities. To me that discrepancy seemed to be more annoying than dramatic. Although, I'm sure there are shows out there that have made this kind of conflict work before, but SaiKano doesn't just didn't do it for me.