I think it's a shame in a way that Matt is leaving, I felt like we were finally starting to see some more depth to his Doctor and emotions other than the silly/funny persona we see so much of. For instance I thought his big speech against the sun god was very well acted, and also when he played the cyber version of the Doctor he portrayed a completely different personality and was quite creepy.
Unfortunately the writing in many of the episodes is quite weak and doesn't really allow the actors to shine. The main problem (IMO) is the writers often try to fit in overly complex stories, which basically results in the episode being rushed and resolved very quickly in the last few minutes, often with the use of 'deus ex machina'. Put simply, the episodes have problems with pacing, and sometimes just don't really make sense.
The other thing that annoys me is the way some of the characters are written, namely the Doctor and Clara. For instance in the Cold War, the way Clara acted made no sense, she wasn't even scared and kept smiling and being all chirpy/jokey. I think this did get better through the series, and to be fair I do like Clara as a companion, but it's as if the writers are trying to fit in all these neat little jokes and quirks, but it kinda gets in the way of the real emotion and story.
Though it probably is about time Matt left, before he gets too typecast or stale, I think there is a real issue with the writing (and perhaps direction) of Doctor Who at the moment. Lots of people just don't watch it anymore, because the stories are much more convoluted and many plot points just go unresolved/unexplained. I often find myself confused or frustrated with the stories, and this isn't necessarily going to change with a new Doctor. It's not that I hate every episode- there were several I quite liked this series- but I do think it's time for Moffat to step aside and let someone else take the reigns.