When comparing Old School Reference and Indexing Compilation (OSRIC) vs Shadowrun, the Slant community recommends Shadowrun for most people. In the question“What are the best tabletop RPGs?” Shadowrun is ranked 23rd while Old School Reference and Indexing Compilation (OSRIC) is ranked 32nd.
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Pros
Pro AD&D 1E aligned to d20 SRD
OSRIC is based on the well-known 1st edition of Advanced Dungeons & Dragons, arguably the most popular RPG of all time. It doesn't stick to is slavishly, though, but instead brings in a few innovations from the later "d20 SRD" to regularize the system a bit and fill in some of the gaps. It is, however, still very much a 1980s system.
Pro In-depth character creation
Cons
Con Complex and inconsistent rules
There is no "general system" for doing things in the game - everything is a special case. This can result in a lot of page-flipping to find the particular rules for something, and in problems for new GMs who don't yet know the system well, or who aren't comfortable with improvising.