The Wraith fleet is fairly unique in the universe as they are almost entirely organic in nature. This gives them certain advantages and disadvantages.
During the war with the Ancients they focused on numbers rather then quality as Ancient weapons could shred anything they could manage to build with their comparatively advanced yet inferior technology to the Ancients. They out numbered the Ancient warfleet five to one, but they were still losing and being pushed back at every turn. Until they captured three ZPM's. They used the energy to grow more ships rapidly, and then they outnumbered the Ancients ten to one.
Wraith vessels are almost entirely geared towards offensive power, another leftover fact from the Ancient/Wraith war. No defenses they could build would be good enough to stop Ancient drone weapons or energy weapons, so they focused on both their weapon effectiveness and the number of weapons on each ship. Wraith vessels are very well armed, class for class Wraith vessels usually have many more DEW's then the vessels other races.
Wraith vessels are not entirely defenseless, their first line of defense is a thick tough exoskeleton armor that is resistant to heat and radiation. The next is their organic ships ability to rapidly regenerate and heal damage. The final is the Wraith EM jamming technology which can block transporters like those used by the Asgard.
The most significant advantage Wraith vessels possess is that fact that they can be grown. Grown very quickly, even quicker with access to a advanced powersource like a ZPM.
The major disadvantage they have is that the Wraith have very inefficient power generation, which is a contributing factor as to why they do not utilize force fields in defense of their vessels.