The Adventures of Batman & Robin for Genesis is an extremely difficult game with repetitive enemy encounters and a very unique soundtrack.
Only through memorization and dedication can one truly survive the punishment that is Contra: Hard Corps, one of the best games in the Contra series.
If you like the Gauntlet games, this entry is amazing and is one of the best 16-bit games you can get.
Thunder Force III is one of the best games for players who are new to the genre or want to get into it. It won’t kick your ass after five minutes of playing and there’s plenty of diversity in the stages and weapons to keep you interested.