I personally think that history will look fondly on LVG. He's been given 3 years to build the foundations of a team for the next decade (Martial, Depay, Herrera, Shaw, Darmian etc.) have the potential to be mainstays in the side for years to come. He's playing the football he feels is necessary to maintain our league position while doing it. Dislike it all you want, but right now, it's effective in the only measure that really matters - points. People act like he's inherently a defensive manager, when he's historically built many attacking sides. He's just pragmatic, and does what he feels is necessary according to his squad's strengths/weaknesses.
He has his methods/philosophy and admirably sticks by them no matter what. At almost every club he's managed at he's attracted the ire of fans/media in one way or another, but he almost always leaves them in a better way than he left them, while winning trophies.
Finally, we've been spoilt by the unprecedented consistent levels of success that Fergie achieved. We're in transition - stop expecting everything while we are. Every big club goes through peaks and troughs - for years at a time. Barcelona, Bayern, Madrid (who last had a GREAT team, when?) etc. all have spent years at a time in the wilderness. Put his performance into the context of what he's been asked to do, rather the unrealistic expectations he's being held to, and judge him then.