And yet the combat sections in Ep2 were nothing more than a shooting gallery.
Nice; that's what combat sections are. The point is that's all most shooters actually do for the entire game; that would be a true shooting gallery.
But it's no longer innovative. It's getting old fast, because it hasn't been drifting away from the FPS genre; it's been stuck in it. It either needs to embrace its genes and improve on the FPS elements or it needs to get rid of them entirely, neither of which is it doing.
You can't put your finger on innovation the way you're doing it right there. That's some flawed thinking. It's drifted entirely away from the FPS genre, most of which have barely begun to break from the mold of doing little more than shooting down enemies. Such mundane and superficial gameplay points don't really exist within Half-life as it is now, save for any point with the antlions, which was pretty dire (especially the caves). It innovates constantly with new approaches to situations; for instance the Strider battle or the auto-gun yard; the chopper/gravity gun scene or the 'run to the Thumpers - all innovation within the gameplay. You can't pin innovation on a single element in any way, shape or form. Innovation is not always smack in your face. It's about diverse, multi-tiered gameplay, and doing something persistently different from the corner you last took; we may have seen a few of the set pieces in EP2 before (namely the physics puzzles and various zombie encounters), but it's still one of the few games that continues to innovate with its gameplay and elevate the core of the game to more of an experience.
To brush it off as "shooting the same kinds of enemies with the sames kinds of guns" is to side with the narrow minded idea that this is all an FPS can achieve. It really isn't and Half-life, along with a few other games, is a testament to that.