Roberts was not one of the elite halfbacks of the NRL, he was probably a mid-ranking halfback who has mostly played in teams at the lower end of the table. He does, however, have a good highlights montage which suggests he has some spark to his game and isn't just a "work the team around the park" kind of halfback, which is why there was some excitement on here when he signed.
He has obviously had injuries and it could be that he is not fully fit and this is restricting the explosive parts of his game in which case he is playing a more limited game at the moment which is fair enough and we can hope to see more excitement from him over time.
Wire fans have high expectations from Aussie halfback signings, but the expectation isn't that they will all be Langer or Johns ability, the benchmark are guys like Greg Mackey and Nat Wood, who bought in to the spirit of the club and became real iconic Wire players. They were at the heart of their teams, lifted the other players and came up with big plays at important moments. Roberts from his NRL pedigree should be a player at least of the Mackey or Wood ability level so if he can show that kind of attitude he will be a very good signing.
The slight niggling fear I have with Roberts is that when I watched his highlights video the player he reminded me of was Denis Moran at London, and I would definitely take that kind of performance. Watching him so far with us, he reminds me of Denis Moran at Wigan. Sometimes these moves don't work out, like Moran didn't for the Pies.