I'm looking forward to seeing what he does with Sonic, after all he's definitely got the FX and CGI experience to pull it off. I was amazed at how much of Deadpool was CGI when I saw the rough cuts.
I don't think it is a case of choosing Sonic over Deadpool though. He was already off Deadpool due to creative differences with Ryan Reynolds (I've heard rumours ranging from budget to who should play Cable and it is a real shame) and just seems to have picked a really interesting project to bounce back with.
I was more than happy with the results of Deadpool since it did match my expectations. Deadpool was different than the rest of super hero movies and I did enjoy watching a different side of super hero life. I am very curious to see what the director will do with Sonic will he bring out a different side of Sonic aswell. I hope it doesn't disappoint since I consider Sonic a classic.