Among various tracks that combined together, there was
1. Super Heavy Launcher - a long term dream since the failure of N1, realised in Energia
2. Reusable crewed orbiter - Buran orbiter
3. Mir-2, the successor to Mir space station - was supposed to use (1) for construction and (2) for crew
4. Fully reusable launch vehicle - was proposed continuation of Energia project
5. various missions requiring super heavy launchers (either Energia, or prospective Vulkan which added extra energia core stage on top) - including mars missions that were on slow boil since end of moon program
6. Soviet Space Forces - anti-SDI systems, orbital warfare unmanned cruisers (Polyot) etc. - dependant on (1).
7. Reduction of space construction and launch costs - nuclear-powered orbital tug launched by Energia which would be responsible for moving objects from low LEO to target orbit, including GEO
1,2,4, and 7 were all included directly in the scope of Buran, with Polyot (6) being in progress as well (the other Energia launch was launch of Polyot test unit).
Note that Buran orbiter, the one part that resembled Shuttle, is independent of other tasks though considered beneficial for the space station goals - if the orbiter project failed, it would still provide data for Reusable Energia variant, and Energia would still mean a working 100t-to-LEO system they could use for whatever - unlike Shuttle which was one specific vehicle. This also meant that Buran's orbiter had much lower cargo capacity - because it didn't need to have higher one as space station modules and the like could just use Energia.
Also, as it became apparent in the meantime, even the Americans didn’t get it right when it came to the reasons behind building the shuttle system. As far as I understood there were other, less expensive ways, that they could have taken in order to “improve” their space program.