While Laertes is bold and rash as he crashes into Elsinore, calling Claudius "O thou vile king! (V,i,116), and while he is gullible in believing Claudius's intention are for Laertes to avenge himself against Hamlet, Laertes does have some redeeming characteristics.
For instance, just before Laertes wounds Hamlet with the rapier whose tip has been poisoned, he has a twinge of conscience as in an aside he says, "And yet it is almost against my conscience (V,ii,296). Then, as he and Hamlet lie dying, Laertes asks Hamlet to forgive him as he forgives Hamlet:
Exchange forgiveness with me, noble Hamlet
Mine and my father's death come not upon thee,
'Nor thine on me! (V,ii, 308-310)
And, perhaps the most redeeming trait of Laertes is his devotion and love for his sister. To Ophelia, Laertes gives sound advice when he learns that she loves Hamlet, cautioning her to remember that he is Prince of Denmark and may have to marry someone else, and to be careful with her affections:
...Perhaps he loves you now,
And now no soil nor cautel doth besmirch
The virtue of his will, but you must fear,
His greatess weighed, his will is not his own,
For he himself is subject to his birth.
He may not, as unvalued persons do,
Carve for himself, for on his choice depends
The safety and health of this whole state,
And therefore must his choice be circumscribed
Unton the voice and yielding of that body
Whereof he is the head. Then if he says he loves you,
It fits your wisdom so far to believe it....[But]
If with too credent ear you list his songs,
Or lose your heart, or your chaste treasure open
To his unmastered importunity.
Fear it, Ophelia, fear it, my dear sister,
And keep you in the rear of your affection. (I,iii,14-34)
That he loves his sister dearly is also evidenced when Laertes jumps into her grave:
Lay her i' th'earth,
And from her fair and unpolluted flesh
May violets spring! I tell thee, churlish priest,
A minist'ring angel shall my sister be
When thou liest howling (V,i,208-212)
Impetuous and at times rather foolish, Laertes is, nevertheless, forgiving and loving.
In Shakespeare's Hamlet, Act 4.7 reveals two not-so-flattering character traits of Laertes.
Claudius hatches a plan, supposedly for Laertes to get revenge on Hamlet for the killing of Polonius, that will enable Laertes to get revenge without appearing to do so on purpose. Claudius will arrange a fencing dual between Laertes and Hamlet, and
He [Hamlet], being remiss [careless],
Most generous, and free from all contriving,
Will not peruse [inspect] the foils, so that with ease,
Or with a little shuffling, you may choose
A sword unbated [unblunted], and in a pass of practice [treacherous thrust]
Requite him for your father. (Act 4.7.132-137)
Laertes, with a "live" sword, instead of a protected one, can stab and kill Hamlet without appearing to have known the tip was unprotected.
Laertes not only goes along with the plan, but adds his own touch, so to speak.
...I will do't,
And for that purpose I'll anoint my sword.
I bought an unction of a mountebank,
So mortal that but dip a knife in it,
Where it draws blood no cataplasm [poultice] so rare,
Under the moon, can save the thing from death
That is but scratched withal.... (Act 4.7.137-144)
Laertes will poison his sword tip, so just in case the wound he delivers to Hamlet is not mortal, the poison will kill him anyway.
Laertes, then, is revealed to be gullible (he is being used by Claudius to get rid of Hamlet for Claudius' own reasons), as well as treacherous.