"Middling effort" refers to a level of performance or attempt that is neither very good nor very bad. It implies that the effort was average or mediocre, without excelling or falling short in any significant way. Full definition
There have been an astounding number of excellent additions to the sports sub-genre (Warrior, The Fighter, Million Dollar Baby, and just last year, Creed, to name but a few) and many more middling efforts to boot. (silverscreenriot.com)
Racing and virtual reality is essentially a match made in heaven yet we PSVR users have seen only handful of releases in the genre and most of them are of middling efforts best left in the past. (thevrgrid.com)
While the series to date has attracted some attention with its splashy camera gimmick, the games themselves have been somewhat middling efforts, saddled with some lacklustre stealth mechanics, and perhaps by the fact that shooting Nazis is so last century. (gameplanet.com.au)