Not sure how this season got the same Metacritic score as last season. There's a world of difference.
They can only watch the first four episodes but even then, I find that Metacritic can sometimes be wrong. For example, Breaking Bad season 1 has a 73, Game of Thrones season 1 is 80 and Mad Men season 1 is 77. Meanwhile, The Walking Dead has been pretty consistent at around 80 for 6 seasons.
It's definitely rare for them to screw up mid-series but it's happened before. For example, Sons of Anarchy season 2 (best one, imo) has an 86 and season 3 has an 84 (very boring season, imo - might be most hated by fans).
I wouldn't put much stock into them when it comes to House of Cards. They're definitely useful though, generally speaking.