No matter how easy it is, it's still an adventure game. In fact, its design is p. much adventure game-y through and through. I've even kinda accepted the art style, and currently think it isn't too bad actually. (See DotT or MI3.)
It's just that it fails to deliver on any of the proper or good adventure game expectations, like complex or entertainting puzzle solutions. (See MI 2 and 3, DotT or, heck, Deponia 2 for examples.) As a result, it does fail as an adventure game - not because it isn't one, but because it's a crappy one. Which makes an entire world of difference.