Wizards - well maybe. Replaying now as a mage.
Not restricted to Wizards but one of the best features in the game is 'Hammer' (you can get level 5 of Hammer in Act II) good, oh yes very good, but slow to cast however combine this the the bow/crossbow and use your DK as a tank with the DK sword (unique item in Act II?) and you should be able to get to nearly the end of Act IV without change.
Have good reports of 'polymorph' but as only at one skill point of this at the start of Act III so cannot comment yet.
Would suggest that you do not rely and any one set of skills (Warrior/Survivor/Wizard) aim for a selected set from each skill regardless of the type chosen at the start of the game and concentrate on building on these.
Good luck
marts
