The first picture was not a good choice, because the tower looks square from it. Otherwise there is nothing obviously wrong on it. I know that the roof is hard to do though, so I will not bother you with that.
Cool! The shape of the tower is awesome, although it's a bit hard to tell that it has five sides in these pictures. Maybe a shot from above would be good? There are some very nice details on the tower, and the landscape looks good too.
I like it a lot, but I think you could have done better. The landscaping was a little dull, maybe you could have added a tree or a pond, and it would have been a bit more attractive with some action in it, maybe show the wizard casting a spell, or maybe even a small battle. It also would have been nice to see an inside to the tower. But all in all, it is a very nice tower. Also, the more pictures the better!