Firstly, sorry for my bad English.
In Season 2, Warwick was kinda OP because the rework of his passive. And also the S2 Items are suitable for him, e.g. Wit's End + Ionic spark works pretty well. For that, Riot gave him some huge nerfes on his Q.
In Season 3, we have Vi. Her ultimate is similiar to Warwick's. Compared to Warwick, Vi clears jungle faster, does much more damage, and the S3 itemizations are much suitable for her. Therefore, I don't see any reasons that I should pick Warwick, instead of Vi.
How to be a good Wawick? Build tanky, higher attack speed, higher CDR, and higher MS. then you will feel his strength. But in S3, I don't see any great items for him. Frozen Heart got nerfed. Wit's End got nerfed. Ionic Spark got deleted...
As a Warwick's lover. I have some suggestions for Warwick recently.
1) Need more good tanky & attack speed items
2) Buff back Warwick's Q
3) Buff his jungle speed