It is unfair to compare the series with the movie -- so often critics will score low any adaptation that lacks the power of the original. So I will start by saying that my disappointment did not come from there.
Even though Ritchie directed both the movie and the series, the movie is tighter and more cohesive. The series in my opinion is an example of style over substance.
Theo, portrays the lead character whose narrative arc begins as a soldier, lacks any apparent emotional or romantic connections, who drifts along a criminal path and wholeheartedly embraces ruthless murder by the end. Are we meant to cheer when his moral decay leads to the cold-blooded execution of his rivals?
The inclusion of the wonderful Giancarlo Esposito in the plot is wasted, as we are expected to believe that this criminal mastermind happily embraces imprisonment at the end. Really?
Others have commented on the comedrama elements of the series. However, Ritchie employs this technique lazily, and assumes the audience is fully onboard, happily embracing the nudges and winks. When there is no emotional investment in the characters however, no one cares.