Greek fan of V-Span here been watching him all play year long he was my favorite player in the Greek league.
Spanoulis is a combo guard who's main weapon is penetration and speed, i've seen him do some acrobatic layups and quick, effective if not flashy crossovers. He has an explosive first step and good basketball IQ and can play defense and steal the ball(as he did in the European league last second thriller semifinal against Tony Parker's France).
The best comparison in the NBA that i can think of is actually Tony Parker though he doesn's score as much.
I just hope he gets playing time in order to adjust to the NBA, i think he can be a good NBA level player, just don't expect him to make a difference from the first season