The phrase "bland level" refers to something that lacks flavor, excitement, or interest. It suggests that whatever is being described is plain, uninteresting, and dull. Full definition
The later games in particular had a weird combination of great graphics, extremely bland level design, really crappy boss fights, and long, excessively difficult platforming sections. (gameological.com)
The over complicated controls and bland level design ultimately eat away at the rest of the achievements. (metacritic.com)
It's a lot better than Episode 1, but there are still a few nitpicky details, such as bland level design in some levels, as well as unnecessarily hard special stages. (metacritic.com)