It's not a good time to be a Half-Life fan, and Dota 2 is taking the heat for it. Just days after Half-Life fans started swarming the Dota 2 Steam page with negative reviews, the Recent Reviews rating for Valve's most popular game is now down to "Mixed," meaning less than 70% of the reviews are positive. As of press time, these reviews are actually down to 62% positive.
Of course, there's the ever-present reality that Half-Life 2: Episode 3 is likely not going to happen, but this was made especially painful in the last month when Valve announced a brand new game, that was actually a Dota 2-themed card game, and then a Half-Life writer revealed what was likely a working script for Episode 3, and it was actually really good. Now knowing what could have been, Half-Life fans were more emboldened than ever to let Valve know how they feel.
While there are people who legitimately despise Dota 2, Half-Life fans included, most people are actually upset at Valve for simply focusing all their attention at supplementing their popular MOBA game rather than develop new titles. Whether or not this is a fair response, it's certainly a loud and clear one. Only time will tell if Valve actually heard it.