Your nearest modern equivalent to SOR and GA for single player would be a game like Ninja Gaiden imo (I can only vouch for the original as I have not played part 2), or the next game due for release by the Ninja Gaiden creator (who has left the studio responsible for the franchise).
I know it might not seem so at first but Ninja Gaiden imo is the perfection of the beat-em-up genre that SOR is also a part of, and combines the same elements (graphics, sound, fight engine) to make a spectacular experience.
If you are looking for a remake of the original SOR, check this:
http://www.bombergames.net/sorr_project/ - its quite a swish update and retains the 2D feel.
Was really let down by Part 3. Check out the remake I posted above - its quite the thing