The early iD games were good - Wolfenstein and Doom. The first of three episodes in each were shareware, and were complete games in their own right. IIRC the complete boxed games were about $20 and available only mail order. At the time they were pretty innovative shooters.
Duke Nukem was another in the genre that was innovative and had substantial free content.
Duke Nukem was another in the genre that was innovative and had substantial free content.