His appellate rights are severely limited following sentencing after a plea, especially if the plea is part of a plea agreement when he knows that the sentence was the result of mutual agreement. Thus, he can not challenge discretionary aspects of sentencing.

His appellate rights after sentencing will pretty much be limited to whether his plea was voluntary, and not induced by coercion or misrepresentations. This will be difficult to prove as a guilty plea colloquy involves detailed questioning of the defendant asking him whether the decision to plead guilty is voluntary, in his best interest, discussed with counsel who answered any questions he may have. Further the defendant must state that he's pleading guilty because he is, in fact, guilty of each charge, the elements of which have been explained to him. He will be advised of his right to trial, that a unanimous jury must find him guilty beyond a reasonable doubt and by pleading guilty this right is waived. There are also questions to establish that he is not under the influence of medication, drugs or alcohol, such that his present judgment is not impaired.

So in the end all the bases are covered.