I think Ashton Kutcher has suffered in the public  eye because of some roles he's had, because he's a pretty boy, and because he married an older woman.
I also think The Guardian proved he is able to act.
I also think Charlie Sheen has been coasting for a long, long time based on earlier successes.  I think he's too drugged up most of the time to do his job, and I think what he was doing on 2 1/2 men was really not very good acting - in fact I thought he looked very distracted and uninterested in what he was doing.  His work was sloppy and lacked effort and commitment.  With good writers and co-stars, he has coasted for a very long time.
If it had been someone else other than Sheen doing that work, it would have been very heavily criticized.
On the other hand Jon Cryer really has thrown himself into his role and worked his tail off to do a great  job.  Every single second on camera he is doing 150%.  He's brilliant and he deserves every penny he gets.   The young actor who plays his son is so natural and relaxed, he is nothing short of amazing.
I would like to see the writers have more guest actors come on.  I think that would be great and help keep people guessing about what will happen next.   It's a heck of a lot better than people tuning in because Sheen is a drunk mess and he's playing a drunk mess on the show.
I think Sheen's two co-stars on 2 1/2 and the lady who plays their maid are absolutely brilliant comedic actors and that the writers can write very, very well.
I also think that Kutcher should be able to join the cast and given a little time to jell, wind up part of a very, very good comedy team.
The show will change.  It had to.   Sheen is just not capable of working, being reliable, showing up every day and doing a decent job.  
But it's a lot worse than that.  By keeping him on the show, his boss and the entire crew were 'enabling' him, in other words helping him to keep drinking and drugging.  
Hopefully no one else will give him a job til he gets cleaned up.  Otherwise he is an absolute mess and is going to kill someone or someones.  People like him don't change after one brief session in Rehab. His problems run much deeper than that and it's going to take a long time and a lot of ups and downs for him to stay sober.  He is extremely manipulative and very good at blaming other people for his problems.   And he gets way, way too much support and attention from the public.
I don't think it's ethical to enable someone to keep destroying themselves, their family, and endangering everyone else around him, just because he's doing a tv show people like.  That is disgusting, it went on long enough.
Hollywood is changing.  Actors and their addictions are catered to less and less.  Schedules are tight and more is expected of them.