Lizardmen armies are a wide and colorful mix of units, with an emphasis on close combat and defeating the enemy through a combination of superior arms, attrition and a huge selection of monsters. The backbone of the Lizardmen, the Saurus units, are a cut above other infantry units in terms of resilience, especially if properly supported with the faster, nimbler skinks and heavy hitters. They also have a lot of fliers, cavalry and skirmishers, providing maneuverability.
That being said, the Lizardmen are geared towards offense, rather than defence: poor selection of missile infantry reduces effectiveness during sieges, while a lack of area of effect artillery makes them vulnerable to wave attacks (though they are excellent when it comes to eliminating small, high health and armor units). Do note that several of their units suffer from rampage if they are severely damaged, removing them from player control.