The thing with Lucas is that he does not have a flashy tackle to show the fans unlike mash or Gerrard, but what we fail to see is how well he is positioned and gets in there and nicks the ball off.
The other thing is his composure on the ball (sometime he does get overpowered, like the Drogba incident) but you can t say he is POOR because of one incident.
Looking at the passing stats(guardian chalkboards) from Chelsea game, he had 40 successful passes compared to 5 unsuccessful ones; and he was playing quite deep as well.
Looking at the tackles, he went in for 13 and won 7 while loosing out 6
Compare that to Mikel, who had one tackle to show for; similarly Essien went in on 9 and won 6 of them (most of them (4) were in the flanks, so it could be throws, and runs which are easier to cover for). Lucas tackles were very central.
Looking at interceptions made, Liverpool made 26, 5 were made by lucas in the DM area. mikel had 1 and Essien 1
Lucas conceded 2 freekicks the whole match, one at the centre circle and the other just outside the box late on.
So, you can analyse urself what Lucas brings in