It is possible to argue that the character of Faustus is used to do both of these things. On the one hand, it is clear that Faustus is a character who is captured by a massive ambition that is impressive, even though it simultaneously reveals him to be an arrogant man. Note, for example, the following quote in Act I scene 1 where he talks about the power he will gain:
All things that move between the quiet poles
Shall be at my command: emperors and kings
Are but obeyed in their several provinces;
But his dominion that exceeds in this,
Stretcheth as far as doth the mind of man;
A sound magician is a demigod:
Here, tire my brains, to gain a deity.
Faustus is to be admired for the extent of his ambition and the totality of the power he craves. In one sense, therefore, he can be seen as a celebration of the spirity of the Renaissance, with its focus on human possibility and potential and its spurning of God's authority and ultimate will. Faustus is an example of Renaissance man taken to it extreme: he deliberately rejects God's power and control over his life to gain his own power and wealth, and is successful.
However, at the same time, critics have pointed out that although Faustus is a character that strikes the audience as impressive at the beginning of the play, once he has his power, he reveals what a petty individual he is. He only uses his power to perform parlour tricks and to amuse himself. Having such amazing power, he seems at a loss to know what to do with it. Indirectly, Marlowe uses this to criticise the way in which Renaissance beliefs extolled the possibility in man at the expense of forgetting divine realities. Certainly, Marlowe, at the end of the play, has to pay the price for doing away with God, however temporarily, by facing the consequences of his actions. This play can therefore be seen as both a criticism and a homage to Renaissance man, in all of his glory and weakness.