Well, he has been a very consistent hitter the last several years. He has hit over .300 every year since 1997. The one thing to be concerned with would be his injury history. If Walker is healthy, I have no doubt that he will hit .300-30-100. He is especially helped by playing in Coors.
He is hitting .238 right now. That is a bit slow but nothing to worry about. Within a month, that should be up around .300.
He was hitting about .100 the first week+ of the season but has rebounded nicely. He's at .391 fort the last week with an OPS over 1.400. I believe they were on the road for much of this past week as well. Don't worry about Walker's hitting, just his health.